Course 08 · Blades, Guards and Tool Care · Lesson 1 of 12
How do blade numbers relate to cutting length?
Higher blade numbers generally leave shorter coat, but exact lengths vary by maker, so always check the blade chart.
Blade numbers relate to cutting length in a general, inverse way: a higher number usually leaves a shorter cut, and a lower number usually leaves a longer cut. A blade numbered 30 leaves coat very short, a blade numbered 10 leaves a short but more visible length, and a blade numbered 4 or 5 leaves a noticeably longer length. The exact length left, however, varies by maker, by blade type and by whether the blade is a standard, skip tooth or finishing blade, so the number alone is not a precise measurement. Always check your own blade chart, and test on a small area first.
Why do numbers work backwards?
Blade numbers come from a traditional system in which the number describes the blade design, not a direct length in millimetres. Over time, makers settled into a pattern where higher numbers cut closer, because the teeth are finer and the blade sits closer to the skin. Lower numbers, with wider teeth and a greater cutting distance, leave more coat. The pattern is consistent enough to be useful for choosing, but it is not a universal scale, and two blades with the same number from different makers can leave slightly different lengths. Some blades also carry letters, such as F for a finishing blade with finer teeth that leaves a smoother finish, or a skip tooth design that feeds thick coat more easily but can leave tracks. Read the full blade description, not just the number, and keep the maker chart with the blade.
What lengths do common blades leave?
The table below gives approximate, general lengths for common detachable blades, to help you understand the scale. These are starting points only, and your maker chart is the authority for your blades. Lengths are approximate because coat type, growth direction and guard use all change the result.
| Blade | Approximate length left | General character |
|---|---|---|
| 40 | Very close, under 1 millimetre | Surgical and detail use, not home body work |
| 30 | Very short, about half a millimetre to 1 millimetre | Close detail, needs teaching |
| 15 | Short, about 1 millimetre | Close, for detail areas with guidance |
| 10 | Short, about 2 millimetres | Common base blade for guard work |
| 7F | Medium short, about 3 millimetres | Finishing blade, smoother finish |
| 5F | Medium, about 6 millimetres | Longer maintenance length |
| 4F | Medium long, about 9 to 10 millimetres | Longer finish, needs preparation |
| 3F | Long, about 13 millimetres | Longest common finishing blade |
A blade used alone gives the length in the table. A blade used with a guard leaves more, as Lesson 2 explains. Do not rely on memory for these figures. Keep the chart, and check it when you buy a new blade, because a new maker or a new blade type can shift the scale.
How do blade types change the result at the same number?
A finishing blade, marked F, has fine, closely spaced teeth and leaves a smooth, even finish, which suits a body coat that will be seen. A skip tooth blade has wider spaced teeth that let thick or matted coat feed through more easily, but it can leave tracks and is not a first choice for a smooth home finish. A standard blade sits between the two in character. At the same number, a skip tooth blade may look rougher than a finishing blade, even though the nominal length is similar. For home maintenance, a finishing blade, or a standard blade with a guard, usually gives the most predictable, even result. Skip tooth blades belong with groomer guidance, because their feeding action and track risk need experience to manage safely.
How should you choose a blade number at home?
Choose by the length you want to leave, the coat type, and your experience, in that order. For a first home clip, a short base blade with a guard, such as a 10 blade with a medium guard, is a common, forgiving combination, because the guard sets the length and the blade provides a consistent base. Avoid very short blades alone for body work, because they leave little room for error and expose skin to heat and nicks. Avoid very long blades alone until you know how your coat responds, because a long blade can drag in thick coat and leave an uneven finish. If you are unsure, start longer, test a small area, and shorten in a later session. Length removed cannot be restored, and a longer first clip teaches you more about the coat than a short clip that must grow out.
What mistakes do beginners make with blade numbers?
Beginners often assume a higher number means longer, choose a blade by number alone without checking the maker chart, or buy a blade that does not fit their clipper system. They may also use a blade alone when a guard was needed, or fit a guard over the wrong base blade and expect the guard label to hold. Another common mistake is to keep using a blade that has become dull, because the number is right but the edge is not, and the result is pulling, tracks and heat. Check the number, the type, the fit, the chart and the condition together, every time, and treat a blade as a system, not as a number on its own.
What can a blade number not tell you?
A blade number cannot tell you whether a coat suits clipping, whether the coat is ready, whether the blade is sharp, or whether your technique is safe. Those judgements come from coat knowledge, preparation, blade care and hands-on teaching, covered in the other lessons in this course and in the clippers course. A number is a useful shorthand for length, and a chart is a useful reference, but neither replaces looking at the coat, feeling the blade, checking heat and watching the dog. Use numbers to plan, and use your eyes, hands and stop rules to decide in the moment.
Further reading
- Pet grooming equipment guidance: manufacturer instructions
- American Kennel Club: grooming guidance