How to use a try square for accurate marking
Updated: October 2026
You have measured the length of a shelf and now need a clean 90° line before cutting. The key to how to use a try square is simple: press the stock against one straight reference edge, keep the blade flat on the face, and take every connected mark from the same prepared faces. The five products in the [try square comparison](/hub/measuring-and-marking-tools/try-square) differ in length, scale and marking aids, but the registration method is the same. Check the tool first, choose a marker that will not damage its edge, and stop if the stock or blade moves.
You have measured the length of a shelf and now need a clean 90° line before cutting.
You have measured the length of a shelf and now need a clean 90° line before cutting. The key to how to use a try square is simple: press the stock against one straight reference edge, keep the blade flat on the face, and take every connected mark from the same prepared faces. The five products in the try square comparison differ in length, scale and marking aids, but the registration method is the same. Check the tool first, choose a marker that will not damage its edge, and stop if the stock or blade moves.
Our top picks
| Badge | Product | Stated length | Marker | Edge | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  WORKPRO WORKPRO 200 mm try square | 200 mm | Pencil | Stainless, sharp in reviews | 9.2 | about £11.99 | View offer |
| Preis-Tipp |  S & S PRODUCTS S & S 150 mm try square | 150 mm | Pencil | Aluminium | 8.2 | about £4.49 | View offer |
| Alternative |  Prexiso PREXISO 250 mm try square | 250 mm | Scriber or pencil | Aluminium on the attribute | 8.7 | about £16.99 | View offer |
On this page
Put the stock on the reference edge
The thicker stock sits against the edge of the board, and the thinner blade extends across the face. Dust, a splinter or a rounded corner can hold the stock away and move the line even when the square itself is accurate.
Hook the stock over the reference edge and press it into full contact without twisting the blade. Draw one fine line. If you are cutting to length, mark the waste side so you know where the saw kerf belongs. A 150 mm S & S can cross a narrow batten. It will not span a 190 mm flooring plank, so choose a longer square rather than extending a short line by eye. The try square buying guide sets out that length trade-off.
Choose a knife, pencil or built-in scriber
A sharp pencil is the safest general marker. Keep it upright so the point follows the same side of the blade. A marking knife gives a finer line. Axminster advises placing the knife's flat back against the square, and only against an edge that can tolerate it. Do not assume a metal-coloured blade is hardened steel.
PREXISO's attribute says aluminium, while a reviewer describes a steel blade and an aluminium stock. Another warns that a utility knife will cut the straight edge. Use the screw-in scriber or a pencil in the 5 mm notches. Those notches are not a depth gauge. Check the first offset with a rule before you repeat it. WORKPRO says its edge is passivated, yet UK reviews describe a razor arris and one cut finger. Do not slide a bare finger along it.
Carry the line around from the same faces
Establish two adjacent reference faces and mark them clearly. Start with the stock against the first straight edge and draw across the first face. Turn the board and register the stock against the same prepared relationship, not whichever edge is nearest.
Carry the line onto the next face by aligning the blade with the end of the existing line. If the final line misses the first, investigate the faces, the square and the technique. Do not average the mismatch. For a shoulder 60 mm from the end, measure once on the reference face, square that line, then transfer it with the stock still on the marked surfaces. Measuring 60 mm independently on all four faces creates four chances of a different result.
Do not use the blade as a lever or the stock as a mallet. If the square has fallen or the joint clicks, follow how to check a try square before the next cut line.
Know what the vial and title cannot do
A short vial gives a quick indication over a small surface. It does not replace a spirit level, and these listings do not state a sensitivity figure. Dirt under the stock has a large effect.
A 45° face on the PREXISO or the Presch can mark a simple mitre. None of the five fixed squares can lock a depth the way a combination square can. See try square vs combination square. Gunpla's title mentions rafters and stairs, but the listing does not show a pitch scale. Do not invent roof pitches with a fixed right angle, and do not store the blade under heavier tools.
Common questions
Which part of a try square touches the board edge?
The thicker stock registers against the straight reference edge, and the blade lies flat across the face. Keep both surfaces in full contact without twisting. If dust, a rounded corner or a splinter holds the stock away, the line can be wrong even when the tool is square.
Should you use a pencil or a marking knife?
Use a sharp pencil for general work and uncertain blade materials. A marking knife makes a finer line against a suitable steel edge, with its flat face registered to the blade. Do not knife against soft aluminium. One PREXISO review warns that a utility blade can cut the edge.
How do you carry a line around a board?
Establish reference faces, mark the first line with the stock against a trusted edge, then turn the board and continue from the same reference relationship. Align each new line with the previous one. Do not measure the same distance independently on every face unless the job demands it.
What are 5 mm notches used for?
They guide a pencil or scriber at repeated offsets from the stock. PREXISO lists 5 mm notches, which can speed parallel marks. Verify the first offset with a rule and keep the stock firmly registered. The notches are marking aids, not an adjustable depth stop.
Can the built-in vial level a shelf?
It can give a quick indication, but its short reference length and unspecified sensitivity make it a poor substitute for a dedicated spirit level. Use a longer level for fitting shelves or cabinets. Dirt under the square's stock can also distort the reading.
When should a competent person take over?
Get appropriate help when the job moves from marking a simple 90° or mitre to structural stair, roof or load-bearing layout. These fixed squares do not provide a rafter pitch scale. A product title that mentions rafters does not supply the design information needed for safe structural work.
Related pages
Sources
Public UK sources for this comparison. Prices, stars and review counts are the amazon.co.uk figures in the listing files, not a live reload.
- BSI, BS 3322:1981 — carpenters' squares and bevels (retrieved 16 October 2026)
- BSI, BS 939:2007 — engineers' squares (retrieved 16 October 2026)
- Wonkee Donkee Tools — engineer's square accuracy (retrieved 16 October 2026)
- Wonkee Donkee Tools — how to use a try and mitre square (retrieved 16 October 2026)
- Wood Workers Workshop — flip test (retrieved 16 October 2026)
- Axminster — measuring and marking (retrieved 16 October 2026)
- Axminster — types of woodworking square (retrieved 16 October 2026)
- Consumer Rights Act 2015, section 22 (retrieved 16 October 2026)
- Faithfull — carpenters' try squares (retrieved 16 October 2026)