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Chisel size affects both the quality of the cut and how much control you have over the tool. A wide chisel removes waste quickly, but it is awkward in a narrow hinge recess. A small chisel fits tight corners, yet it can take too long to chop a large mortise and is easier to damage if you twist it.
For most carpenters, a useful working set is not a dozen sizes. Four or five bench chisels, plus one narrow, sturdy chisel for rough work, will cover ordinary mortises, hinges, joinery, and general repairs.
The Basic Chisel Sizes to Own
Chisel widths are normally stated in millimeters, although many sets also use inches. The most useful sizes are 6 mm (1/4 inch), 10 mm (3/8 inch), 12 mm (1/2 inch), 18 mm (3/4 inch), and 25 mm (1 inch).
| Chisel width | Best uses | Main limitation |
|---|---|---|
| 6 mm / 1/4 in | Small hinges, narrow grooves, corners, fine paring | Slow for removing much waste; prone to bending if abused |
| 10–12 mm / 3/8–1/2 in | General joinery, medium hinges, small mortises | Not wide enough for efficient broad paring |
| 18 mm / 3/4 in | Typical door hinges, medium mortises, general bench work | Too wide for tight corners and small hardware |
| 25 mm / 1 in | Large mortises, broad paring, trimming shoulders | Needs room and is less precise in small recesses |
If you are buying your first set, a bench chisel set in these common sizes is usually better value than buying unusual widths individually. A set also gives you matching handle shapes and steel, though individual replacement chisels may make more sense later.
Choosing Chisels for Mortises
Match the chisel width to the mortise width, but do not expect one chisel to do every stage. For a 12 mm mortise, a 10 or 12 mm chisel is suitable. For a 19 mm mortise, an 18 mm chisel is the practical choice. A chisel slightly narrower than the mortise can clear the bottom without rubbing both walls.
Start by chopping a series of cuts inside the waste area, leaving roughly 1 to 2 mm from the layout lines. Drive the chisel bevel-side toward the waste when establishing the wall, then remove the remaining material with controlled cuts. Finish the walls and ends with a sharp edge rather than trying to force the tool through all the waste in one pass.
For a deep mortise, use a mortise chisel rather than a thin bench chisel. Mortise chisels have thicker blades and stronger edges, so they tolerate direct hammer blows and levering along the grain. A 6 mm bench chisel driven hard into a deep mortise can mushroom at the striking end, bend, or chip at the edge.
A mortise chisel should usually be somewhat narrower than the mortise itself. For a 1/2-inch mortise, a 3/8-inch or 1/2-inch mortise chisel works well, depending on the timber and the amount of waste. The wider option removes more material, but the narrower one is easier to control at the corners.
Choosing Chisels for Door Hinges
Hinge recesses are commonly about 3 inches long and 3 to 4 inches wide, but the required chisel size depends on the hinge leaf and the corner radius. An 18 mm (3/4-inch) chisel is a good general hinge choice. A 12 mm (1/2-inch) chisel handles narrower leaves and gives better control near screw holes. Keep a 6 mm (1/4-inch) chisel for cleaning the hinge corners.
Do not try to square rounded hinge corners with a wide chisel. First mark the corners with a knife, then pare toward the lines using the narrow chisel. On painted or finished doors, score the perimeter deeply before chopping. Otherwise, the finish can lift beyond the hinge outline.
For occasional door work, a standard 3/4-inch bench chisel is enough. A dedicated heavy-duty or bevel-edge hinge chisel is worthwhile if you install doors regularly, but it is not necessary for a homeowner fitting one or two hinges.
Bench Chisels Versus Mortise Chisels
Bench chisels are thinner and lighter. They are better for paring, trimming joints, cleaning corners, and general repair work. Their bevels often allow access into tighter spaces, but their blades should not be used as pry bars or driven aggressively through hard stock.
Mortise chisels are thicker, heavier, and designed to take repeated mallet blows. They remove waste quickly and resist twisting. The trade-off is reduced finesse: a thick blade may not fit beside a hinge leaf, into a narrow dovetail, or along a delicate shoulder.
For general woodworking, buy bench chisels first. Add one or two mortise chisels when you regularly cut traditional mortises. A cheap mortise chisel can be perfectly adequate for softwood framing or occasional repairs if the edge is properly sharpened. In hard maple, oak, or ash, better steel and a comfortable handle reduce sharpening interruptions and edge damage.
Width Is Not the Only Factor
Blade thickness matters nearly as much as width. Two 12 mm chisels may behave very differently if one has a thin bench blade and the other has a heavy mortise blade. Check the blade profile, handle, and intended use rather than shopping by width alone.
Edge condition is another major factor. A wide, dull chisel is harder to control than a narrow, sharp one because it requires more force. For ordinary bench work, sharpen to about 25 degrees and add a small secondary bevel around 30 degrees. The exact angle is less important than a flat back, a clean edge, and regular honing.
Look for handles that suit your method. A socket or reinforced handle tolerates mallet work better. A slimmer handle gives better feedback for paring. Metal striking caps are useful on chisels designed for heavy chopping, but they can damage a workpiece if the handle slips or the tool is used carelessly.
A Practical Buying Plan
For a first general-purpose kit, choose 6, 10 or 12, 18, and 25 mm bench chisels. Add a 6 mm or 10 mm heavy mortise chisel if you cut deep joinery. This combination covers hinge recesses, door hardware, cabinet joints, small repairs, and most furniture work.
If your work is mainly site carpentry, prioritize a durable 12 or 18 mm chisel and a compact sharpening system. A heavy-duty chisel set may survive rough framing better, but it will not replace a thin, accurately sharpened bench chisel for finish work.
Buy unusual sizes only when a job proves you need them. A 32 mm chisel is useful for broad paring but unnecessary for most home workshops. Spend the difference on a reliable honing guide or sharpening stones if your current chisels cannot hold a clean edge. Good technique and sharp steel usually matter more than owning every width.