Blade gap, exposure, span, and cutting angle

The 4 parameters that define a safety razor

 

 

By Augustin, founder & craftsman — Atelier DURDAN, Saint-Affrique, France

 

 

When you look for a safety razor, you always come across the same number: the blade gap. 0.70 mm, 0.90 mm, 1.20 mm. It’s the parameter everyone knows, every manufacturer advertises, and most discussions revolve around. “The bigger the gap, the more aggressive / efficient.” We’ve all read it somewhere.

The problem is that it’s an oversimplification. And like any oversimplification, it can lead to poor choices.

I’ve been designing and manufacturing safety razors since 2022, in my workshop in Saint-Affrique, France. Every razor head I draw in 3D relies on four geometric parameters — not just one. The blade gap is one of them, but it’s neither the most important nor the most decisive. To understand how a razor actually shaves, you need to understand all four, and above all, how they interact.

This article is my attempt to lay things out clearly. No marketing jargon, no “aggressive vs mild” rankings. Just geometry, measurements in millimetres, and the experience of a maker who lives with these parameters every day.

The four parameters at a glance:

Cutting angle — the angle between the blade and the skin. It determines whether the blade cuts the hair or scrapes the skin. It’s the first parameter I define when I design a razor.

Blade gap — the height between the blade and the baseplate. It’s the number everyone knows, but it only tells part of the story.

Guard span — the distance between the blade’s cutting edge and the point where the baseplate contacts the skin. It’s the zone of “free” skin that can deform. The most important parameter — and the least known.

Blade exposure — the position of the blade relative to the shave plane. Positive, the blade protrudes: direct feel. Negative, it sits back: smooth feel. It’s the razor’s comfort dial.

How these parameters are measured

Before we go into each parameter, a word on methodology. Because a number without measurement context isn’t worth much.

All dimensions on my razors are defined in CAD, using Fusion 360. That’s where I draw each head, position the blade, and set the cutting angle, gap, span, and exposure. These are theoretical values — the ideal geometry.

Once the first prototype is machined, I physically verify the critical dimensions. The parameter I check first is blade exposure — it’s the one most likely to deviate if the blade isn’t perfectly seated. This check is done under a microscope. To materialise the shave plane (the line between the highest point of the cap and the highest point of the baseplate), I place a precision dowel pin on the assembled razor. It gives me a physical reference line, and I can verify that the blade is tangent to this line — or offset by the expected exposure value. Other dimensions are checked with a digital calliper.

Reference blade. All published dimensions are defined with a specific blade: Feather Professional for Artist Club razors (La Faulx, Horizon), Personna GEM for the Vestige, and Feather or Derby for Double Edge razors (Le Maurice, Numéro 7). Between different DE blade brands, thickness varies by a few hundredths of a millimetre — not huge, but enough to slightly alter the actual cutting angle and exposure. It’s a factor to keep in mind when switching blades.

1. The cutting angle — the foundational parameter

This is the first parameter I define when I design a razor. Before the gap, before exposure, before everything else.

Definition. The cutting angle is the angle formed between the blade and the shave plane — the line drawn between the two contact points of the razor with the skin (the top of the cap and the edge of the baseplate). It’s the angle at which the blade meets the skin.

Why it matters. This angle determines whether the blade will cut the hair cleanly or scrape the skin. It’s a matter of penetration.

A narrow angle (acute) allows the blade to penetrate the skin easily. The slightest ridge of skin passing in front of the edge will be sliced cleanly. It’s efficient — but it’s also what causes nicks, weepers, and micro-cuts. The blade doesn’t forgive.

A wide angle (obtuse) means the blade skims the surface. You scrape more than you cut. It’s safer, but if the angle is too wide, efficiency drops: the hair isn’t sliced at its base, it’s pulled or bent. That’s what causes razor burn and that unpleasant “scraping” sensation.

In practice. My razors range between roughly 25° and 35°. I generally work above 30° — that’s the sweet spot I prefer between safety and efficiency. Below 25° is dangerous on most configurations. Above 35°, cutting quality drops off.

But this isn’t an absolute rule. You can have a narrow angle and a safe razor — provided you control the other parameters tightly. That’s exactly what I did with the Vestige: a relatively narrow cutting angle, offset by a very controlled gap and span. The result: excellent cutting quality, especially on coarse hair — because a narrow angle allows a smoother, cleaner cut without tugging. It’s actually better for the skin: less scraping, a clean cut at the base of the hair, a gentler shave overall.

The trade-off: a narrow angle is far more restrictive on the parameters that follow. The gap must be precisely calibrated, the span must be controlled to the tenth of a millimetre. There’s no room for error — the margin is thin. It’s a design choice that requires everything else to be perfectly dialled in.

Key takeaway: take two razors that are strictly identical in gap, span, and exposure — change only the cutting angle. The one with the narrower angle will feel more aggressive. That’s how important this parameter is, yet it’s rarely mentioned on a product spec sheet.

Don’t confuse: the cutting angle (set by the razor’s design) and the shaving angle (how the user tilts the razor on their face). The cutting angle is fixed — I draw it. The shaving angle is what the user finds by positioning the razor so that the cap and baseplate are both in contact with the skin. Once the right shaving angle is found, the two contact points touch the skin, and the cutting angle does its job.

An important nuance: the role of the blade. The cutting angle as designed by the razor maker is a theoretical angle — it assumes a blade of a given thickness and grind. But not all blades have the same grind angle. A blade with a more acute bevel will reduce the actual cutting angle; a blade with a more obtuse bevel will increase it. In practice, switching blade brands on the same razor can slightly alter the cutting behaviour. That’s one reason why with the same baseplate you can get different shaving experiences — the blade is part of the equation.

Another nuance: the gap changes the cutting angle. When you increase the gap by switching baseplates, you’re not only changing the height under the blade — you’re also mechanically altering the cutting angle. As the gap increases, the cutting angle tends to open up. It’s a geometric effect: the blade’s position relative to the shave plane shifts. Keep this in mind when comparing baseplates on the same razor: you’re never changing just one parameter, even if the gap number makes it look that way.

Cross-section view: cutting angle, gap, span, and blade exposure — the 4 geometric parameters of a safety razor.

2. The blade gap — what everyone knows (and why it’s not enough)

The gap is the measurement you’ll see everywhere. It’s also the simplest to understand and communicate. But that’s precisely why it’s misleading.

Definition. The blade gap is the vertical distance between the blade’s cutting edge and the baseplate, measured at the closest point of the baseplate. It’s the “height” under the blade.

What the gap actually does. The gap determines the space in which the skin can deform. The larger it is, the more room the skin has to bulge under the blade, allowing the hair to be cut closer to its root. A small gap limits this deformation: it’s safer, but the shave isn’t as close.

Why it’s insufficient. The gap only measures a vertical distance, at the closest point. It tells you nothing about the shape of the baseplate beyond that point. And it’s precisely that shape which determines how the skin actually deforms.

Take two razors with an identical gap of 0.60 mm. The first has a baseplate that curves back up immediately after the gap measurement point — the skin has nowhere to go, it’s contained. The second has a baseplate that extends far outward before rising back toward the skin — the skin has much more room to deform, and the razor is significantly more efficient. Same gap. Radically different shave.

In summary: the gap is a useful shortcut for getting a rough idea. It’s convenient for quickly comparing baseplates within the same razor, where other parameters remain constant. But for comparing two different razors, or for understanding why a razor shaves the way it does — the gap alone doesn’t tell the story.

3. The guard span — the parameter nobody explains

This is the most important and least known parameter. If you take away one thing from this article, let it be this: it’s the span, not the gap, that truly determines a razor’s efficiency.

Definition. The guard span is the distance between the blade’s cutting edge and the point where the baseplate contacts the skin. In other words, it’s the length of “free” skin — the zone where skin can deform unsupported — between the blade edge and the first point where the baseplate touches the face.

Where the gap measures a height (vertical), the span measures a distance along the skin surface. It’s a far more representative measurement of what actually happens during shaving, because it’s this distance that determines how much skin can “bulge” toward the blade.

Why it’s the key parameter. The wider the span, the more the skin can deform. And the more the skin deforms, the more the hair is presented to the blade, and the more efficient the shave. It’s a direct mechanical effect, independent of the gap.

But there’s a second, less obvious effect: as the span increases, the amount of skin deforming toward the blade also increases — and with it, the pressure that skin exerts on the cutting edge. More free skin = more pressure on the blade = a closer shave. It’s not just that the hair is “presented” to the blade — the skin is actively pushing against it. This mechanism is why the span has such a marked impact on actual shaving efficiency.

A span that’s too wide makes shaving less forgiving. It takes more skill to avoid nicks, because the skin bulging between the baseplate and the blade is no longer protected. Conversely, a span that’s too small limits efficiency: the razor struggles to cut, especially longer stubble, because the skin doesn’t have enough space to deform and “present” the hair to the blade.

Same gap, different span. Span a (short) vs Span b (long) radically changes the skin deformation zone.

A concrete example: La Faulx. La Faulx is a single-edge Artist Club razor. With the Classique baseplate, the gap is 0.56 mm — a modest number that might suggest a very mild razor. But the span is 2.67 mm. The span-to-gap ratio is nearly 5:1.

Why? Because I designed the baseplate with an extrusion that extends far outward. The gap is small, but the skin deformation zone is very wide. Result: La Faulx in Classique is a remarkably efficient razor despite its modest gap. It’s the span doing the work.

If you went by the gap alone, you’d expect a timid razor. In reality, the span tells a very different story.

The Vestige — span reimagined. The Vestige takes the concept even further. On most razors, the span is read in cross-section — you look at the razor’s profile. On the Vestige, I wanted to create the span in a different direction: across the width of the razor.

The Vestige’s baseplate features large arch-shaped openings distributed along its entire length. Instead of the skin deforming “downward” into the gap (as on a conventional razor), it deforms laterally through these openings. The span is no longer in the cross-section plane but in the width plane.

The principle remains the same: give the skin space to deform and present the hair to the blade. But the direction changes. That’s what allows the Vestige to have a very small gap (0.19 mm in Classique) while still delivering real efficiency — because the span is created differently.

Vestige — lateral span: the arch-shaped openings in the baseplate create the deformation space in a different direction.

4. Blade exposure — the comfort dial

Exposure is the most intuitive parameter for the user to feel. It’s the “blade feel” — that perception of the blade on the skin that makes a razor seem mild or aggressive.

Definition. Blade exposure is the position of the cutting edge relative to the shave plane. The shave plane is the line drawn between the highest point of the cap and the highest point of the baseplate — the two points of the razor that touch the skin.

If the blade extends beyond this line: exposure is positive (measured in mm, e.g. +0.10 mm).

If the blade sits back from this line: exposure is negative (e.g. -0.12 mm).

If the blade sits exactly on the line: exposure is neutral (0 mm).

The triangle and skin deformation. In practice, the blade and the two contact points of the razor form a triangle. The shape of this triangle dictates how the skin interacts with the blade.

Positive exposure — the triangle “points” outward. The blade protrudes. The skin deforms under pressure from the blade and the two contact points. The hair is in direct contact with the edge, effortlessly. The razor is more efficient but also more aggressive: blade pressure on the skin is immediate. The more positive the exposure, the more the blade extends — and the more pressure it exerts on the skin, which also improves closeness. Exposure is therefore not just a comfort parameter: it’s also an efficiency lever.

Negative exposure — the triangle “points” inward. The blade sits back. The skin deforms between the two contact points (cap and baseplate) and has to “reach” the blade. Blade pressure on the skin is reduced. It’s milder, more comfortable — but the skin must deform enough to reach the blade.

Positive exposure (red) vs negative (blue). Skin deformation changes dramatically depending on blade position.

And this is where an often-overlooked factor comes in: skin firmness. Supple skin will deform easily and reach the blade even with negative exposure. Firm skin — thicker, more resistant — may not deform enough. Result: the razor doesn’t cut well enough, not because it’s poorly designed, but because the geometry doesn’t suit that skin type.

This is why some users find a razor “doesn’t shave close enough” while others, with the same razor, are perfectly satisfied. It’s not subjective — it’s mechanical.

In practice across the Atelier DURDAN range

Le Maurice: constant exposure at +0.05 mm, regardless of the baseplate chosen (from 0.80 to 2.00 mm gap). This is a deliberate choice: +0.05 is enough to cut effectively on any skin type. We then adjust efficiency solely through the gap (and therefore the span), without touching comfort. That’s Le Maurice’s core concept: increase efficiency without increasing aggressiveness. Note, however: even though exposure stays fixed, blade feel progresses slightly between baseplates. That’s the span pressure effect — as the span grows, the skin pushes harder on the blade, and you perceive the edge more. It’s not the exposure changing, it’s the mechanical pressure.

Numéro 7: exposure ranges from -0.12 mm (0.30 plate) to +0.23 mm (1.50 plate). That’s the widest range in the lineup. The 0.30 plate with its very negative exposure is extremely mild — almost imperceptible. The 1.50 plate at +0.23 is a very technical experience, reserved for experienced shavers.

La Faulx: exposure from 0 (Classique) to +0.15 (Ultra). The progression is gradual and follows the increase in span — you gain efficiency and blade feel simultaneously with each plate.

Vestige: same exposure progression as La Faulx, from 0 to +0.15, but with much smaller gaps (0.19 to 0.40 mm). The Vestige’s cutting angle is also narrower than on the other razors in the range, giving it that characteristic cutting sharpness — balanced by a very controlled span.

Horizon: from -0.15 to +0.20 in continuous adjustment (positions 1 to 8). It’s the only adjustable Artist Club razor on the market. The span is calibrated from the design stage to be optimal and stays fixed regardless of position. What you adjust is solely the blade exposure — and therefore blade feel and skin pressure. It’s worth noting that exposure doesn’t just affect feel: by increasing blade protrusion, you also increase cutting pressure on the hair, and therefore closeness. It’s a comfort and performance parameter.

5. How the 4 parameters interact

None of these parameters works in isolation. It’s their combination that defines a razor’s character. And that’s where most online discussions miss the point: they isolate one parameter (usually the gap) and try to draw conclusions.

Here’s how I see them interact, as a designer:

The cutting angle sets the framework. It’s the fundamental safety parameter. It determines whether the blade tends to penetrate the skin (narrow angle) or scrape it (wide angle). All other parameters work within this framework. A well-chosen angle gives room to play with span and exposure. A poorly chosen angle makes everything else more critical.

The span determines real-world efficiency. It’s the amount of skin that can deform and present itself to the blade. Wide span = efficient razor that cuts hair close. It’s the parameter I adjust to increase or decrease cutting performance.

Exposure determines comfort, feel, and contributes to efficiency. It’s the razor’s perceived “personality.” Positive = blade-forward, direct feel, increased cutting pressure. Negative = blade-back, smooth feel. It determines whether the razor “has character” or feels “transparent” — but by increasing exposure, you also increase blade pressure on the hair, and therefore closeness.

The gap is the visible consequence of the head geometry. It’s correlated with the span but doesn’t replace it. Useful for comparing baseplates within the same razor (where angle and baseplate shape stay constant), but insufficient for comparing two different razors.

Three concrete illustrations

Le Maurice — efficiency without aggressiveness. Exposure is fixed at +0.05 mm. When a customer moves from the 0.80 to the 1.60 plate, the gap increases — and with it the span. The razor becomes more efficient: it cuts more hair, closer. Blade feel also progresses, not because exposure changes (it stays constant), but because the increased span creates more mechanical pressure on the blade. It’s an increase in efficiency and sensation through the span, without an increase in aggressiveness through exposure.

The Vestige — narrow angle, controlled span. The Vestige’s cutting angle is significantly narrower than on the other razors in the range. In theory, that should make the razor more “bitey.” But the gap is very small (0.19 mm in Classique) and the span is controlled differently — through the lateral openings in the baseplate. The result: very clean cutting quality, particularly effective on coarse hair thanks to that narrow angle, without the risks normally associated. The combination of narrow angle + controlled lateral span gives a razor that is both precise and safe.

Numéro 7 — the widest range. With baseplates from 0.30 to 1.50 mm, the Numéro 7 covers the broadest spectrum. The 0.30 plate (gap 0.30, exposure -0.12) is an extremely mild razor — negative exposure combined with a small span makes the blade almost imperceptible. The 1.50 plate (gap 1.50, exposure +0.23) is the opposite: wide span, strong exposure, very present blade feel. Same razor, same head — but two radically different shaving experiences, because span and exposure change together.

6. What this means for you

If you’re trying to understand a safety razor — or choose your own — here are the questions to ask yourself, in order:

Cutting angle: is it designed for safety or for raw performance? Most manufacturers don’t disclose this angle, but its effects are felt: a razor that nicks easily, even with a small gap, probably has an angle too narrow for your technique.

Guard span: what’s the real distance between the blade and the baseplate’s contact point? A gap number alone won’t tell you. Look at the baseplate shape — if it extends far from the blade, the span is larger than the gap suggests.

Exposure: is the blade above or below the shave plane? If you have firm skin and your razor doesn’t cut well enough, the problem may not be the gap — it’s exposure that’s too negative for your skin type.

Gap: useful for comparing baseplates within the same razor. Less reliable for comparing different razors.

7. In practice — which parameter to prioritise for your profile

Every razor in the Atelier DURDAN range was designed with a set of baseplates covering multiple profiles. The same profile can match different razors with different plates. Here are the broad principles I apply when advising a customer — knowing that the final tuning always depends on shaving frequency, number of passes, and what the customer is looking for in terms of feel and result.

Beginner, sensitive skin, average beard. The priority is safety and ease of use. I favour a short span (the razor is more forgiving of positioning errors), a small gap, and neutral or slightly negative exposure (less risk of nicks if the angle is wrong). In practice: Le Maurice with 0.80 or 1.00 plate, Numéro 7 with 0.30 or 0.50 plate, La Faulx with Classique plate, Vestige with Classique or Medium plate.

Coarse beard, resilient skin, shaving every 2–3 days. This profile generally has no issue with blade feel — their skin handles it well. They mainly need efficiency to deal with several days’ growth. I favour a wider span and positive exposure so the razor has the cutting power required. In practice: Le Maurice with 1.40 to 1.60 plate, Numéro 7 with 0.70 to 0.90 plate, La Faulx and Vestige with Medium or Supérieur plate.

Experienced, chasing the closest shave. This profile has mastered their technique and wants the closest possible shave. We can go for the most technical setups: wide span, strong exposure, pronounced blade feel. In practice: Le Maurice with 1.80 to 2.00 plate, Numéro 7 with 1.10 to 1.50 plate, La Faulx and Vestige with Ultra plate.

These are broad guidelines. In reality, every customer is a unique case — that’s why I offer a personalised consultation form.

Conclusion — why a gap number alone means nothing

The safety razor industry has settled into a habit: communicating the gap as if it were the only parameter that matters. It’s understandable — it’s simple, it’s a number, it’s easy to compare. But it’s an incomplete picture.

A safety razor is a geometric system. The cutting angle defines safety. The span defines efficiency. Exposure defines comfort and contributes to efficiency. And the gap is only a partial reflection of the head geometry.

At Atelier DURDAN, every razor is designed by working these four parameters together. That’s what allows Le Maurice to increase its efficiency without increasing its aggressiveness. That’s what allows the Vestige to have a narrow angle and a safe shave. That’s what allows La Faulx to be remarkably efficient with a gap of 0.56 mm.

Next time you read a gap number, ask yourself: what is the span? What is the exposure? What is the cutting angle? Because without those three other parameters, a gap on its own only tells the beginning of the story.

 

Atelier DURDAN

High-end safety razors, CNC machined to order

Saint-Affrique, Aveyron, France