What is a rafter square used for?+
A rafter square is a triangular layout tool used by carpenters and framers to mark plumb cuts, seat cuts, birdsmouth cuts, and hip and valley angles on roof rafters. It also functions as a saw guide for cross-cuts on dimensional lumber, a try square for checking 90° corners, and a pivot for marking any angle from 0° to 90°. The pitch scales etched on most rafter squares let you read the rafter angle directly from the rise-over-run without trigonometry.
What is the difference between a rafter square and a speed square?+
"Speed Square" is a brand name registered by Swanson Tool in 1925. Today it’s used generically for the same triangular layout square most carpenters call a rafter square. Functionally they’re the same tool — a 7-inch right triangle with a fence on one leg. Some manufacturers call theirs a rafter square to emphasize the rafter-cut markings; Swanson calls theirs a Speed Square because of the brand. The Rapid Rafter Pro is the modern dual-sided version of both.
What is the best material for a rafter square?+
For framing crews, polymer composite (like the Rapid Rafter) and machined aluminum are the two best options. Polymer is lighter, won’t conduct heat in summer, and won’t corrode. Aluminum is heavier and more rigid but can deform if dropped or compressed in a nail bag. Polycast plastic (like the Empire 296) is the cheapest material but flexes under load and degrades in direct sun. Steel rafter squares exist for shop use but are too heavy for daily framing.
What size rafter square should I buy?+
A 7-inch rafter square is the standard size for residential framing — it covers 2x lumber, fits in any apron, and works for 99% of framing cuts. A 12-inch rafter square is useful when you’re marking 2x12 floor joists, 4x4 posts, or LVL beams in one pass. Most framers carry the 7-inch and reach for a framing square (24-inch) for the rare wider cut. The Rapid Rafter Pro adds expandable 3", 4", and 6" base plates that turn the 7-inch tool into a 12-inch when needed.
How do you read a rafter square?+
Hold the rafter square with the fence (the lipped edge) flat against the lumber. Pivot the square on the fence corner. The Common scale on the long edge shows the rafter pitch in inches per foot of run (3/12, 6/12, 8/12, 12/12, etc.). The Hip-Val scale runs alongside — read it for hip or valley rafters of the same pitch. The degree scale on the hypotenuse shows the actual angle in degrees. For a plumb cut, mark along the long edge at your pitch number; for a seat cut, mark perpendicular to it.
Is a 7-inch rafter square big enough for framing?+
Yes — 7-inch is the standard for almost all residential framing. The 7-inch leg lets you mark across a 2x6 (5.5" actual width) with room for the fence to register. For 2x10 (9.25") and 2x12 (11.25") joists, you either flip the square or use a 12-inch model. The Rapid Rafter Pro’s 6" expandable base extends the 7-inch tool to handle double 2x assemblies, 6x6 posts, and 6" LVL beams without switching to a framing square.
Why does the Rapid Rafter mark both sides of a board?+
Traditional rafter squares are single-sided — you mark one face of the board, flip the square (or the board), and mark the other side to complete a square cross-cut. The Rapid Rafter’s patent-pending design has fences on both edges, so a single pass marks both faces simultaneously. On a roof with 60 rafters that’s 60 fewer flips. It’s the only design change to the rafter square in nearly a century — Popular Mechanics named it Gear of the Year 2025 specifically for that reason.