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The speed square is the single most useful marking tool for a beginner, and it takes two minutes to learn. A basic one costs about 8 to 20 dollars and does three jobs: it marks dead-square lines, reads any angle for miters, and — its underrated superpower — guides a circular saw through a perfectly square crosscut. There’s nothing to it and nothing hazardous. The whole trick is the raised fence lip: hook it over the edge of the board and the tool references that edge automatically, so your line or your saw cut comes out square without measuring a single angle.
Tools and materials
- A speed square (7-inch is the common size) and a pencil — that’s the whole kit for marking.
- A circular saw if you’ll use the square as a cut guide — see our best circular saws and straight-cut guide.
- These squaring skills feed nearly every project — a sawhorse, a bench, or crown molding.
Step 1: Understand the fence
One edge of the speed square has a raised lip — the fence. Hooked over the edge of a board, it seats the tool square to that edge every time. This is what makes the speed square fast: you reference the board’s own edge instead of measuring angles. Press the fence firmly against the board so there’s no gap.
Step 2: Mark a square crosscut line
Hook the fence over the board edge and run your pencil along the square’s perpendicular edge. The resulting line is automatically 90 degrees to the edge. Slide the square along and repeat if you need a line all the way around a board. Keep the fence tight to the edge the whole time or the line drifts.
Step 3: Guide the saw for a square cut
For crosscuts up to about 7 inches wide, hook the fence over the edge, hold the square down firmly, and run the flat base of your circular saw against the thick perpendicular edge of the square as you cut. The fence keeps the square from slipping, so the saw is guided dead-square with no offset math. This is the fastest guided crosscut there is.
Step 4: Lay out an angle
To mark a miter, keep the pivot corner (by the fence) hooked on the board edge and swing the square until the degree mark you want on the diagonal scale lines up with the board’s edge. Then draw along the square’s edge. Forty-five degrees gives a corner miter; other marks give any angle you need. The pivot-and-read move turns the square into a protractor.
Step 5: Use it to check for square
Beyond marking, hold the speed square into a corner of an assembly to confirm it’s a true 90 degrees before you fasten — invaluable when gluing up a box or a frame. A quick check with the square as you assemble catches out-of-square joints while you can still fix them.
Where to go next
Squaring is the foundation for clean cuts everywhere — combine it with our straight-cut guide and put it to work on a sawhorse or workbench. It all lives under the power tools and workshop hub.
We never buy or physically test the tools we rank — our picks come from aggregated owner reviews and expert consensus, explained on how we rank.