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Guide · Layout · Speed squares, framing squares, combination squares and torpedo levels

What does a 4/12 pitch look like on a speed square, and how does it differ from a framing square? Reading pitch and rafter angles, combination squares, L-squares and the 3-4-5 check, torpedo levels, magnetic levels, and the sizes of each

A 4/12 pitch rises 4 inches for every 12 inches of run, which is 18.4 degrees; on a speed square it is the 4 on the common-rafter scale along the long edge: pivot the square on its corner against the board edge until the 4 lines up with the edge and the hypotenuse marks the cut. A speed square (rafter square) is a 7 or 12 inch aluminum triangle with a lipped fence, a 45 degree edge, a degree scale and rafter scales; a framing square (L-square, carpenter’s square) is a flat 24 by 16 inch L with rafter tables stamped on it, for laying out stair stringers, rafters and checking large work square. A combination square is a 12 or 16 inch rule in a sliding head with 90 and 45 degree faces and a bubble, for marking, depth and short squareness. A torpedo level is a 9 inch level with a magnetic base for pipe, conduit and metal.

Bayshore Safety. Industrial safety, roofing tools and jobsite supplies since 2017. · Current as of November 2026 · the C&R product data on this site (M-004 7 in aluminum alloy square; M-014L 24 x 16 in all-metal L-square; M-016 16 in combination square; MCL-290 9 in torpedo level with magnetic base); the scales printed on a rafter (speed) square (common, hip/valley and degree scales) and the geometry of pitch (rise over 12 in of run; 4/12 is 18.4 degrees, 6/12 is 26.6, 8/12 is 33.7, 12/12 is 45); the 3-4-5 rule
Squares and levels we stockAll roofing tools
C&R M-004 Aluminum Alloy Square, 7 inC&R M-004 Aluminum Alloy Square, 7 inThe product data lists the M-004 as a 7 in aluminum alloy square
$5.18See the product

Pitch, in one line. Roof pitch is rise over 12 inches of run: 4/12, 6/12, 12/12. The speed square carries that number on its common scale so the angle never has to be converted to degrees, and the framing square carries the rafter tables so the rafter length per foot of run can be read off. The cards below answer what 4/12 looks like on the square, how to find a roof angle with it, the difference between the squares, what an L-square and a combination square are for and their sizes, the 3-4-5 check, whether a framing square has a 45, how to adjust one, what a torpedo level does, and what size it comes in. The magnetic level is here because it is the level roofers and gutter crews use on metal.

Squares and levels, question by question

Sizes are from the product data on this site; the pitch angles are geometry, and the scales are the ones printed on every rafter square.

What does a 4/12 pitch look like on a speed square, and how do you find a roof angle with one?Hold the square with its lipped fence tight against the edge of the rafter stock, pivot point (the corner marked PIVOT) at the edge, and swing the square until the number 4 on the COMMON scale lines up with the board edge; the long edge of the square now lies at the 4/12 angle, 18.4 degrees from the fence, and a pencil along it marks the plumb cut. To find an existing roof’s pitch, set a level horizontal with one end touching the roof, measure 12 inches along it from that end, and measure down to the roof: that distance in inches is the pitch (4 inches is 4/12). Or lay the speed square on the roof with a torpedo level on its fence and read where the roof line crosses the common scale. The common pitches: 3/12 is 14.0 degrees, 4/12 18.4, 5/12 22.6, 6/12 26.6, 8/12 33.7, 10/12 39.8, 12/12 45.
What is the difference between a speed square and a framing square, and what is a rafter square?Speed square, rafter square and triangle square are the same tool: the aluminum triangle with a fence, in 7 inch (the pocket size, our M-004) and 12 inch. It marks 90 and 45 degree cuts off its fence, any angle from the degree scale, and rafter plumb and seat cuts from the common and hip/valley scales; it is also the saw guide for a circular saw. A framing square is the big flat L (24 by 16 inches, our M-014L), with no fence; it lays out stair stringers (rise on one leg, run on the other), checks large assemblies and door frames for square, marks birdsmouths and rafter lengths from its tables, and squares sheet goods. Both have 45 degrees: the speed square on its hypotenuse, the framing square by the equal-leg method (the same number on both legs at the edge gives 45).
What is an L-square used for, and what size is an L-square?L-square is the general name for the framing square and for its small relatives (the 8 by 12 inch try-type squares) and large ones (the 24 by 16 carpenter’s square and the 48 inch drywall T-square); a steel L-square at 24 x 16 is the carpenter’s framing square. Uses: squaring a corner on a sheet or a frame, laying out stairs, marking a square cut across a wide board, checking a roof bracket plank or a window opening, and as a straightedge. Its scale is inches in 8ths and 16ths on one side and the rafter and brace tables on the other.
What is a combination square, what do you do with it, and what size should I get?A rule (12 inch standard; 16 inch on our M-016; 6 and 24 inch also sold) that slides through a cast head with a 90 degree face and a 45 degree face, a bubble level and often a scriber. Uses: mark a square line across a board, mark a 45, set the rule to a depth and scribe a line parallel to an edge (the most used function on a jobsite), check a depth or an inside corner, set a saw blade height, and level a short run. Its drawback: the rule locks with a thumb nut and slips if the nut is not tight, and a cheap head is not square; check a new one by marking a line, flipping the head and marking again, and the two lines must coincide. 12 inch for a pouch, 16 inch for layout. A try square is the fixed version; a sliding T-bevel copies any angle.
Does a framing square have a 45 degree angle, and how do you adjust a framing square?Not as a face; a framing square is 90 degrees only, and 45 is found by setting the same number on each leg against an edge (8 and 8, or 12 and 12) so the diagonal is 45. The speed square has the 45 built in. Adjusting a framing square that is out of true: lay it against a straight edge, mark the line, flip it, mark again; if the lines diverge, the square is open or closed. The old method is a center punch on the inside corner (to open it) or near the outside corner (to close it), one light tap at a time, checking after each. A square that has been dropped on its corner is the usual reason.
What is the most accurate square for woodworking, and what are the squares called?We do not rank; the accuracy classes the square manufacturers publish are what matter: a machinist’s combination square is ground to a few thousandths over its length, a stamped carpenter’s square to about 1/32 inch over 24 inches, and a 7 inch aluminum rafter square is a layout tool, not a reference. Names: speed, rafter, triangle or quick square (the triangle); framing, carpenter’s, steel or L-square (the big L); combination square (rule and sliding head); try square (fixed small L with a wood or steel stock); drywall T-square (48 inch T); sliding T-bevel (adjustable angle); center square; the Japanese square (sashigane).
What is the 3/4/5 rule for squares, and who invented the speed square?The 3-4-5 rule checks a square or a corner over a distance longer than the tool: measure 3 units along one side and 4 along the other from the corner; the diagonal between the marks is 5 if the corner is square. It works at any multiple (6-8-10, 9-12-15 on a slab) and is the chalk-line crew’s check; the chalk line guide linked below covers it. The speed square was patented in 1925 by Albert J. Swanson, a carpenter, and his company still makes it; the name is a trademark that became generic for the rafter square.
What is a torpedo level, what is it good for, and what size is it?A short level, 6 to 12 inches with 9 inch the common size (our MCL-290 is 9 inches), tapered at both ends like a torpedo, with level, plumb and 45 degree vials; many have a magnetic base and a V-groove so they sit on pipe and conduit. Uses: plumbing pipe runs, electrical conduit and boxes, strut, gutters and drip edge (a 9 inch level checks the fall every few feet), window and door shims, appliance feet, and anything a 24 inch level cannot fit into. Pipefitters carry one with a magnetic base and a V-groove; a torpedo level for pipefitters is that pattern. It is not for long runs; a 4 foot level or a laser is.
What is a magnetic torpedo level, and does it matter?The same level with a rare-earth or ceramic magnet strip in the base so it holds itself to steel pipe, conduit, strut, metal studs, gutter and metal roofing while both hands do the work; on a gutter run it rides along the lip as the hangers are set. For wood-only work the magnet does nothing and adds cost; for anything on metal it is the feature that gets used. The magnet sweeper guide linked below covers the other magnetic tools people search with it.

Squares and levels in plain words

  • Pitch is rise over 12 inches of run. 4/12 is 18.4 degrees, 6/12 is 26.6, 12/12 is 45.
  • On a speed square, pivot on the corner and line the pitch number on the common scale with the board edge; the long edge is the cut.
  • Speed square: 7 or 12 inch triangle with a fence; marks 90, 45, any degree and rafter cuts; saw guide.
  • Framing square: 24 x 16 inch flat L; stairs, rafters, big squareness; 45 by equal numbers on both legs.
  • Combination square: sliding rule for square, 45, depth and scribing parallel lines; tighten the nut and check it.
  • 3-4-5 checks square over any distance.
  • Torpedo level: 9 inches, level, plumb and 45 vials; magnetic base for pipe, conduit, gutter and metal.
  • A dropped square is out of true; check by mark, flip, mark.

Questions people ask

What does a 4x12 pitch look like on a speed square?

The long edge set at the 4 on the common scale, 18.4 degrees off the fence.

What is the difference between a speed square and a framing square?

The speed square is a 7 or 12 inch fenced triangle for marking cuts and rafter angles; the framing square is a 24 x 16 inch flat L for stairs, rafters and large squareness.

What is the most accurate square for woodworking?

We do not rank; a machinist’s combination square carries the tightest published tolerance, a carpenter’s square about 1/32 inch over 24 inches.

What is an L-square used for?

Squaring corners and sheets, laying out stairs and rafters, marking square cuts across wide boards, and as a straightedge.

What is the 3/4/5 rule for squares?

Measure 3 and 4 along the legs from the corner; a 5 diagonal means the corner is square, at any multiple.

What is a drawback of the combination square?

The rule slips if the thumb nut is loose, and a cheap head may not be square; check it by mark, flip, mark.

Who invented the speed square?

Albert J. Swanson, a carpenter, patented it in 1925.

How to adjust a framing square?

Check it against a straightedge by mark, flip, mark; a light center-punch tap near the inside corner opens it, near the outside corner closes it.

What size is a torpedo level?

6 to 12 inches, with 9 inches the common size.

What is a combination square?

A 12 or 16 inch rule in a sliding head with 90 and 45 degree faces, a bubble and a scriber.

What is the size of an L-square ruler?

24 x 16 inches for the carpenter’s framing square; smaller try squares and a 48 inch drywall T-square also exist.

Does a framing square have a 45 degree angle?

Not as a face; set equal numbers on both legs against an edge to get 45.

What does a torpedo level do?

Checks level, plumb and 45 on short work: pipe, conduit, gutters, drip edge, shims.

What is another name for a speed square?

Rafter square, triangle square or quick square.

What is the difference between a rafter square and a speed square?

None; speed square is the trade name that became generic for the rafter square.

How do you find a roof angle with a speed square?

Lay the square on the roof with a torpedo level on its fence and read where the roof line crosses the common scale, or measure the rise over 12 inches of run with a level.

What size combination square should I get?

12 inch for the pouch, 16 inch for layout.

What is the torpedo level for pipefitters?

A 9 inch level with a magnetic base and a V-groove that sits on pipe and holds itself there.

Related guides

Chalk lines and marking chalkColors, permanence and lumber crayonsHow do you read a tape measure?Fractions, the 16 and 19.2 inch marks, accuracy and measuring wheelsRoof brackets, roof jacks and ladder accessoriesAngles, planks, hooks and stabilizersMagnet sweepersNail cleanup after a roof jobSaw blades and TPIHacksaw, circular and reciprocating blades

The ratings, test results and standards shown here are the manufacturers' published values, reproduced as published. Nothing on this page is a recommendation by Bayshore Safety that any product is suitable for a particular task, hazard or workplace. Selecting safety products and protective equipment is the responsibility of the end user and the employer, based on their own hazard assessment and the regulations that apply to their work. Confirm every value on the manufacturer's own documentation before use.

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