This page is about choosing. What each kind of square does, and how its error grows along a line, is covered in the square guide; checking one is in how to measure and mark accurately.
Note— How this guide was made
It compares types of square and their published specifications. No square was tested for it, no product is ranked, and no price or rating appears.
First square by the work
| Work | Square | Why |
|---|---|---|
| Furniture and joinery at the bench | A combination square, 12 in or smaller | Squares and mitres lines, and sets and repeats distances |
| Fine joint layout and checking | A fixed try square or engineer’s square | One fixed joint, nothing to lock or creep |
| Framing, decking and site work | A speed square | Hooks the edge, guides a circular saw, gives 45° without setting |
| Large panels, carcasses and frames | A framing square, alongside a smaller square | Long blades show error across a wide surface |
| Checking other squares and machine set-ups | An engineer’s square with a stated tolerance | A reference you can trust more than the tool you are checking |
Many workshops start with a combination square and add a fixed square once they cut joints regularly.
Specifications to check
| Specification | Why it matters | How to check |
|---|---|---|
| Stated squareness | The only accuracy figure that matters for a square | Look for a squareness figure with its length — Starrett states 0.0015 in over 12 in for its combination square; many makers state none |
| Scale accuracy | Matters only if you read distances off the blade | Do not confuse it with squareness: Woodpeckers states its scales to ±0.004 in but gives no squareness figure |
| Fixed or adjustable | A fixed square cannot creep; an adjustable one does more jobs | Match it to the table above |
| Blade length | Longer shows more error and spans wider work; shorter is handier | The widest board you need to square, and the smallest joint |
| Head material and lock | A combination square’s accuracy depends on its head seating | Starrett contrasts cast-iron and forged steel heads with plastic and die-cast ones; the lock should hold without creeping |
| 45° face | Saves setting a bevel for mitres | Combination and speed squares have one; try squares usually do not |
| Readability | Scales you can read are scales you will use | Engraved or etched graduations last longer than printed ones |
| Inside corner | Dust or a burr in the corner lifts the blade | A relieved corner, as on Veritas’s precision square, seats over debris |
What matters less than it seems
- A tighter tolerance than your work needs. A layout square good to a few thousandths over its length is already finer than a pencil line.
- Extra functions you will not use. Levels and centre heads are useful for some work and clutter for other work.
- Appearance. Rosewood and brass do not make a blade square; the joint between blade and stock does.
New or second-hand
A second-hand square is only a bargain if it is square. Old try squares with loose rivets and combination squares with worn heads are common. Check any used square with the flip test before paying for it, and treat a square that cannot be checked as unknown.
Checklist
Before buying a square
- You know which job it is for: joint layout, general bench work, site work or checking.
- The maker states squareness, with the length it applies over — or you can check it yourself before relying on it.
- Any stated figure is a squareness figure, not only a scale figure.
- On an adjustable square, the head locks firmly and seats cleanly on the blade.
- The blade is long enough for your widest parts and short enough for your joints.
- The graduations, if you need them, are clear and durable.
- On a used square, the flip test shows no error you can see.
The other marking choice most people get wrong is the pencil: see how to choose a pencil for woodworking.
Sources
This guide is specification-based: it compares types of square and what makers state, and no square was tested for it. Accuracy figures are the makers’ own, in the form each uses.
- 1.
Frequently Asked Questions on the Starrett Combination Square. L.S. Starrett Company.
Used for: An advertised accuracy of 0.0015 in over 12 in for a 12 in combination square.
- 2.
Combination Squares. L.S. Starrett Company.
Used for: Cast-iron or forged, hardened steel heads contrasted with plastic and die-cast heads; the combination square’s range of functions.
- 3.
20-12 Master Precision Square. L.S. Starrett Company.
Used for: An engineer’s square stated square to 0.0001 in every 6 in, hardened and not graduated.
- 4.
Veritas Precision Square. Veritas Tools Inc..
Used for: Accuracy stated as 0.001 in per inch of length; graduated legs; a relieved inside corner that seats over saw whiskers.
- 5.
Precision Woodworking Square. Woodpeckers.
Used for: A scale-accuracy figure (±0.004 in over the scale) and a repair-or-replace promise, without a numerical squareness figure.
- 6.
Speed Square. Swanson Tool Co..
Used for: A 7 in square combining try square, mitre square, saw guide, line scriber and protractor.
About this buying guide
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.