Chisel Sizes Explained

A chisel's size is simply the width of its cutting edge. A 1/2 in chisel measures half an inch across the edge; a 6 mm chisel is six millimeters across. Sets are sold as a run of widths, but the honest truth is that two or three of them do almost all the work, a few more are genuinely handy, and the rest are mostly there to make the box look full.

The common widths

Western chisels are usually sold in imperial fractions: 1/8, 1/4, 3/8, 1/2, 3/4 and 1 in are the standard run, with wider blades of an inch and a quarter or more available for bench and framing work. Metric sets cover the same ground in round millimeters — roughly 3, 6, 10, 13, 19 and 25 mm — and Japanese chisels are almost always sold in metric.

The conversions are not exact, and they do not need to be. A 6 mm chisel is a hair under 1/4 in; a 13 mm is a whisker over 1/2 in. Nobody measures a joint to the chisel; you pick the width that fits the cut and register off your layout lines, not off the number stamped on the blade.

The two or three that do the work

If you watched which chisels wear their edges fastest, it would be the 1/4 in and the 1/2 in. Between them they handle the overwhelming majority of furniture and cabinet joinery: chopping and paring dovetails, cleaning tenon shoulders, trimming to a knife line, cutting small housings. The 3/4 in and 1 in come out for wider paring and cleanup — flushing a plug, paring a broad shoulder, registering across a flat — and the 1/8 in earns its keep only in fine, closely spaced joinery.

This is why so many experienced woodworkers, asked what to buy, say to start with four: 1/4, 1/2, 3/4 and 1 in, adding narrower or wider sizes only when a specific job demands them. The reasoning behind that short list is laid out in how many chisels do you need, and it is the same logic that shapes our best chisels for beginners picks.

Matching width to the joint

The rule behind the table is simple: match the width to the narrowest part of the cut, then use it for everything up to that size. A 1/4 in chisel cleans a 1/4 in mortise and also pares a wider shoulder; a 1 in chisel is wonderful across a broad flat and useless in a narrow socket. When in doubt, the smaller chisel is the more versatile one, because it fits places the wide one cannot. Which family of chisel you reach for matters as much as the width — chisel types compared covers when a bench, mortise or paring chisel is the right tool at any given size.

Imperial or metric — it barely matters

People agonize over whether to buy imperial or metric chisels, and it is one of the least important decisions in the shop. You are not building to the chisel's stamped size; you are cutting to lines you scribed, and any chisel narrower than the cut can clean it. Buy whichever system your preferred maker sells in, and if you end up with a mixed drawer of 6 mm and 1/4 in chisels, nothing bad happens.

Why big sets oversell

A boxed set of ten or twelve chisels looks like value, and for a lot of buyers it is a trap. Half those sizes will barely be touched, the money spread across twelve blades usually means thinner steel and worse finishing than the same money in four good chisels, and you still have to flatten and sharpen every one before it cuts. Four quality chisels you actually use beat a dozen mediocre ones that mostly sit in the tray.

Buy the sizes the work demands, buy them well, and add to the run only when a real job asks for a width you do not own. That is the buy-it-once path — our best wood chisels guide is built around a small core of sizes chosen to be kept for life, not a big box chosen to look generous.