Walk any framing site in the country and you will find the same tool riding in every apron: a stout triangular square, usually seven inches on a side, with a lipped fence along one edge. Carpenters call it a rafter square, a triangle square, or a speed square depending on where they learned the trade. Whatever the name, it is the most-used layout tool in carpentry, and using it well is one of the fastest ways to make your cuts cleaner and your framing tighter.
What a rafter square actually is
A rafter square is a right triangle with a raised fence, or lip, along one of the short sides. That fence is the whole trick. Hook it over the edge of a board and the long marking edge automatically sits at 90 degrees to that edge. The hypotenuse carries degree markings, so the same tool that squares a cross-cut can also lay out any angle from 0 to 90 degrees by pivoting off the fence. Most squares also carry common and hip-valley rafter tables, scribe notches, and a ruler scale along the marking edge.
The design has barely changed in about a century. It works because it is simple: one reference edge, one marking edge, and a fixed 90 degrees between them. Its main limitation comes from the same simplicity, which we will get to below.
The four jobs it does every day
1. Squaring cross-cuts. This is the bread and butter. Hook the fence over the edge of a 2x4, 2x6, or 2x8 and strike a line along the marking edge. That line is perpendicular to the edge the fence is riding, which is what makes the cut square.
2. Marking angles. Hold the pivot point (the corner where the fence meets the marking edge) tight against the board edge, then swing the square until the edge of the board lines up with the degree you want on the hypotenuse scale. Strike your line. This is how framers lay out rafter plumb cuts, stair stringers, and any miter they plan to cut with a circular saw.
3. Guiding a circular saw.A rafter square is thick enough to act as a straightedge fence for a circular saw. Hold the square firm with your off hand, ride the saw's shoe against the marking edge, and you get a cut that tracks straight instead of wandering off the pencil line. It is the fastest way to get chop-saw quality from a hand-held saw.
4. Layout marking. The scribe notches and ruler scale let you run a line parallel to a board edge, mark repeated offsets for joist and stud layout, and check assemblies for square as you go. On a deck frame or a stud wall, the square never leaves your hand.
Step by step: marking a square cut on a 2x4
- Measure and tick. Pull your tape from the good end of the board and make a single V-shaped tick at your length. A V points at the exact dimension; a fat pencil dash can be an eighth of an inch wide all by itself.
- Seat the fence.Hook the square's fence over the edge of the 2x4 closest to you and slide it to your tick. Make sure the fence is flat against the edge along its full length, not rocking on a splinter or a knot.
- Strike the face line. Hold the square down with firm pressure and draw your pencil along the marking edge in one pass, through the tick. Keep the pencil at a consistent angle so the line does not drift away from the steel.
- Carry the line over the edge. If you are cutting with a hand saw, or you want to track the blade on a thick cut, wrap the line: hold the square against the top edge of the board and connect the face line across it.
- Mark your waste side.A quick X on the off-cut side of the line saves you from the oldest mistake in the book: a perfect cut on the wrong side of a perfect line, which leaves the board a blade's width short.
Pro tips that separate clean framers from rough ones
- Keep your pencil sharp or run a mechanical pencil. A dull carpenter's pencil can throw a line a full sixteenth.
- Always cut on the waste side of the line and leave the line. The line is your dimension; the kerf belongs to the scrap.
- Register the fence on the same edge of the board for every mark on that piece. Lumber is rarely perfectly uniform in width, so switching reference edges mid-layout invites error.
- Check your square once in a while. Strike a line, flip the square over, and strike again from the same reference edge. If the two lines diverge, the tool has taken a hit and needs replacing.
- Watch for wane and rough edges. A square is only as true as the edge its fence is riding. If the board has a waney or rounded edge, see our guide on marking boards with wane or rough edges.
One habit worth building early: mark every face the blade will exit. A single face line is fine for a shallow cut, but on a 2x rip or a deep cross-cut, a line on both faces and the edge tells you instantly whether the blade wandered. That is more marking work with a traditional square, which is exactly the problem the tool below was built to solve. For the full comparison of tool types, read rafter square vs. speed square.
Where the Rapid Rafter fits in
Every technique above assumes a single-sided square: mark one face, then reposition the tool to carry the line over the edge and down the far face. The Rapid Rafter is a patented dual-sided square (U.S. Patent No. 11,654,545 B1) that removes those extra steps. In the open position it straddles the board and marks three sides of any 2x material in one motion: both faces and the top edge, with a perfect perpendicular line regardless of the quality of the board. Fold it flat and it works as a normal everyday square, so nothing about the fundamentals changes.
It was invented by master carpenter Peter Toomey of Liberty Hill, Texas, who has been building since 1984 and founded All Seasons Decks & Gazebos. The Original is made in the USA from a proprietary polymer blend, and the tool earned Popular Mechanics Gear of the Year 2025 and the LBM Journal 2026 Innovation Award. You can see the motion itself on our how it works page.