Speed Squares

A speed square is a flat, triangular layout tool with one edge machined as a fence that hooks against a board's edge, letting you mark a square (90°) or 45° line in a single motion without measuring or aligning a separate straightedge. It's a construction-trade staple — the name comes from how much faster it is than a traditional try square for repetitive framing layout — but it's genuinely useful in a woodshop too, for anything that doesn't need machinist-level precision.

What it's actually good for

• Fast crosscut layout — hook the fence against a board's edge and draw a square line in one motion, faster than aligning a combination square for the same mark.
• A cutting guide for a circular saw — the same fenced edge that guides a pencil also guides a circular saw's shoe for a quick, reasonably accurate crosscut without a full straightedge setup.
• Reading roof pitch and marking angles — the printed degree scale (and, on many models, a pivot pin for marking rafter angles) is genuinely useful for framing-adjacent work, less so for furniture.

Material and size

Aluminum is the standard, lightweight and durable enough for regular use; some are polycarbonate, lighter still but less rigid over time. 7" is the common size for general use; a 12" "rafter square" version exists for larger layout work but is overkill for most shop tasks.

Where it's not precise enough

Fine furniture joinery, anything where a fraction of a degree matters, or checking a machine setup — a speed square's tolerances are built for framing speed, not machinist precision. For that level of accuracy, see Machinist Squares instead.

A cheap accuracy check

Same principle as checking any square: hook it against a known-straight edge, mark a line, flip it over, and mark again from the same point. Any gap between the two lines reveals the error — worth doing once on a new speed square before trusting it for anything that needs to actually be square.