Dog Clipper Blades Explained: A Groomer's Guide to Numbers, Lengths and Types

If you are new to the salon floor, the blade drawer can feel like a foreign language. All those little numbers stamped into the steel, half of them seeming to go backwards, and a client asking for "a number four all over" when what they actually want is a fluffy teddy. Once the system clicks though, it stops being a puzzle and becomes second nature, and you will be reaching for the right blade without even looking. So let me walk you through how I think about blades, the way I wish someone had explained it to me when I started.

What the numbers actually mean

Here is the bit that trips everyone up at first. On a standard blade the number is not the length it leaves, and the higher the number, the shorter the cut. It feels back to front, but there is a logic to it once you stop fighting it.

Think of the number as roughly how fine the finish is rather than how much coat you are keeping. A #10 leaves a very short, close cut of around 1.5mm. A #7 leaves more like 3mm. A #4 leaves around 9mm to 10mm, which is why it gives that soft, plush look owners love on doodles. As the number climbs from 4 up to 30, the cut gets shorter and shorter, right down to surgical closeness.

A rough working guide I keep in my head:

• #30 and #40: surgical prep close, mainly for pads, sanitary areas and under mats where you need to get right down.
• #15 and #10: close working blades, brilliant for faces, feet, sanitary trims and clean lines.
• #7 and #7F: a tidy short body clip, around 3mm, very popular for practical low-maintenance trims.
• #5 and #5F: a touch longer than a 7, a good middle ground for a short but not shorn body.
• #4 and #4F: the plush 9mm to 10mm finish, lovely on curly and wool coats.
• #3 and #3F: the longest of the standard snap blades, leaving the most coat while still being a proper clip.

Get much longer than a #3 and you move away from bare blades altogether and into comb attachments, which I will come to in a moment.

The letters after the number

You will notice some blades carry an F, and occasionally an FC or ST. The F stands for finish, and it matters more than people think.

A finish blade has more teeth packed closer together, so it leaves a smoother, more even cut with fewer tracks and ridges. That is what you want for the visible body coat on a pet trim, especially on anything going to a show-style finish. Without the F you have a skip-tooth blade, which I will explain properly below because the two are genuinely different tools for different jobs.

Skip-tooth versus finish blades

This is one of the most useful distinctions to have straight in your head.

A skip-tooth blade has alternating long and short teeth, giving a slightly gappy cutting edge. That gap lets the blade bite into dense, matted or heavy coat without clogging or stalling. It is your rough-out blade, the one you reach for on a thick, tangled, or unwashed coat to take the bulk off before you refine. The trade-off is that it leaves a coarser, less even finish, and because those longer teeth sit further from the skin you have to be careful, they can catch and nick if you drive them straight into loose skin.

A finish blade (the F versions) has full, evenly spaced teeth for a smooth, closed cut with no tracking. This is your finishing tool once the coat is clean, brushed out and manageable. On a dog that is bathed and fluff-dried, a finish blade over the body gives that clean, professional result with none of the choppy lines a skip-tooth can leave.

My rule of thumb: skip-tooth to fight through the mess, finish blade to make it beautiful. On a matted dog you might rough out with a skip-tooth, then, if the coat allows, go back over with the finish equivalent for a tidier result.

Safety note: Skip-tooth blades and the very close blades (#30, #40) heat up fast and sit close to or right on the skin. Always test the blade against your wrist between passes, keep the skin taut and flat, and never run a hot blade over thin skin, wrinkles or the belly. A blade that is too hot to hold is too hot for a dog.

Snap-on A5 blades versus adjustable blades

Broadly you will meet two systems, and understanding both saves a lot of confusion when you switch clippers.

Snap-on A5 blades are the detachable steel blades most professional detachable clippers take. You pop one off and click the next straight on, changing length in seconds without stopping to fiddle with a lever. This is the workhorse system in most salons because it is fast, the blades are interchangeable across many machines, and you build a drawer of set lengths you know intimately. The A5 fitting is close to an industry standard, so a blade from one detachable machine will usually fit another, which is very handy.

Adjustable-length blades, the kind you find on a five-in-one or an adjustable-lever clipper, use a single blade with a lever that shifts it through a small range of lengths, roughly from a #9 up to a #40 equivalent. They are convenient for quick tweaks on faces and feet without swapping blades, and they suit lighter or all-rounder machines. The limitation is range: you cannot get anywhere near a #3 or #4 body length out of an adjustable blade, so for longer plush trims you are back to snap-ons or comb attachments.

Most groomers I know run a detachable A5 machine as their main clipper for the range and speed, and keep an adjustable five-in-one for detailing.

Guide combs and attachment combs

When a client wants length, more than a bare #3 gives you, this is where comb attachments earn their keep. These clip over a short finish blade (usually a #30 or #40 underneath) and lift the coat to a set length before it is cut, giving you a soft, even, scissored-looking finish across the body.

They come in a graded set, often labelled in millimetres or in their own numbering, and they are the secret behind those long, plush teddy trims that a bare blade simply cannot produce. The key is a clean, well-brushed, fluff-dried coat underneath, because a comb attachment will drag, skip and leave tramlines on anything damp, dirty or matted. Rough coat in, rough result out.

Blade care so they last and cut kindly

A sharp, clean, well-oiled blade cuts better, runs cooler and is far kinder to the dog. Blunt blades pull rather than cut, which hurts. Get into the habit of brushing the hair out of the teeth, oiling the blade little and often during a groom, using a blade wash to clear gunk, and sending blades off to be professionally sharpened before they start dragging. A tidy blade drawer is a sign of a groomer who takes their finish seriously.

Groomer's tip: Label a small tray with your most-used lengths and keep those blades oiled and ready before your first dog arrives. Reaching mid-groom into a jumble of unlabelled, unoiled blades is how you lose time and end up running a blunt blade over a nervous dog. Prep the drawer, not just the dog.

Frequently asked questions

Why does a higher blade number mean a shorter cut? On standard blades the number reflects the fineness of the cut rather than the coat you keep, and by convention it increases as the cut gets shorter. So a #30 is far shorter than a #4. Comb attachments and the #3 to #7 range cover most pet body lengths, with the very high numbers reserved for close work.

When should I use a skip-tooth blade instead of a finish blade? Reach for a skip-tooth to rough out dense, dirty or matted coat where a finish blade would clog and stall. Once the coat is clean, brushed and manageable, switch to the finish (F) version of the same number for a smooth, track-free result on the visible body coat.

Are A5 snap-on blades interchangeable between clippers? Generally yes. The A5 detachable fitting is close to a standard across most professional detachable machines, so a blade from one will usually snap onto another. Always check the fit is secure and the blade seats flush before you run it, and keep to the same brand type where you can for consistency.

What length does a number four blade leave? A #4 leaves roughly 9mm to 10mm, the soft plush finish owners often want on doodles and curly coats. The #4F finish version gives a smoother result than the skip-tooth. For anything longer you move on to comb attachments over a short finish blade.

For further reading around tools and coat types, the Wikipedia entry on dog grooming covers clipping and stripping in general terms, the hair clipper article explains how the cutting mechanism works, and the Royal Kennel Club has sound breed and coat guidance to inform your length choices.

Written from the salon floor by Lucy, City & Guilds Level 2 & 3 qualified groomer and owner of Fluffs, a one-to-one dog grooming salon in Wigginton, York. For more professional grooming guides, explore the Fluffs grooming blog.