150 mm or 300 mm combination square
Updated: 22 October 2026
The product photos for a 150 mm combination square and a 300 mm square often fill the same frame, so the shorter one looks full-size until it arrives. You are choosing 150 mm, 300 mm, or both, for the timber in your hand. Prices are the amazon.co.uk saved listings of 19 October 2026, used in the [combination square comparison](/hub/measuring-and-marking-tools/combination-square). Peter F. did not measure every blade in a lab. A qualifying purchase can earn us a commission at no extra cost to you. Head metal and the standards that do not apply sit on the [combination square buying guide](/hub/measuring-and-marking-tools/combination-square/sub/combination-square-buying-guide).
The product photos for a 150 mm combination square and a 300 mm square often fill the same frame, so the shorter one looks full-size until it arrives.
The product photos for a 150 mm combination square and a 300 mm square often fill the same frame, so the shorter one looks full-size until it arrives. You are choosing 150 mm, 300 mm, or both, for the timber in your hand. Prices are the amazon.co.uk saved listings of 19 October 2026, used in the combination square comparison. Peter F. did not measure every blade in a lab. A qualifying purchase can earn us a commission at no extra cost to you. Head metal and the standards that do not apply sit on the combination square buying guide.
Our top picks
| Badge | Product | Blade length | Single or set | Stock and rule | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  WORKPRO WORKPRO combination square, 300 mm | 300 mm / 12 in | Single | Zinc alloy head, 2 mm stainless rule | 8.5 | about £25.91 | View offer |
| Best value |  Faithfull Faithfull combination square, 150 mm | 150 mm / 6 in | Single | Cast and machined stock, stainless rule | 8.2 | about £6.99 | View offer |
| Alternative |  Faithfull Faithfull combination square twin pack | 150 mm and 300 mm | Set of two | Cast and machined stock, stainless rules | 7.5 | about £19.91 | View offer |
On this page
What 150 mm is actually for
A 150 mm square, often sold as 6 in, belongs in a pouch and on small joinery. It will sit in a hinge recess and mark a narrow rail where a 300 mm head is in the way. Faithfull FAICS150 is £6.99, 99.8 g, and 4.5 from 1,551 reviews. Buyers who wanted a normal square call it tiny. They are describing the photo, not a fault in the 150 mm specification. Tracer ACSQ150 is the other single 150 mm listing, at £15.83 and 160 g, and its written reviews are a shared block with the 300 mm Tracer file.
A 150 mm blade also loses part of its length inside the head, so it will not set a fence across a sheet.
What 300 mm reaches
A 300 mm square, often sold as 12 in, is the one you pick up for skirting, architrave on the bench, and a layout line on a sheet. WORKPRO W064028 is 300 mm and 410 g at £25.91, with 4.7 from 5,203 reviews. Stanley STA046151 is the cast-iron 300 mm at £23.78 and 430 g. Tracer ACSQ300 is listed at £24.00, but the review texts in the file are the 150 mm block, so judge it from the title length, not from those stars.
Part of the blade sits in the head on every one of these. Wirecutter's rule of thumb for a 12 in combination rule is a bit over 10½ in of reachable line, about 267 mm. Treat that as their observation, not as a measurement of WORKPRO or Stanley. A 300 mm square is the wrong tool in a hinge recess.
A twin pack is two squares
A twin pack in this folder is two complete squares, each with its own head, not one rule and a spare stock. A true 150 mm square does not prove the 300 mm square in the same box. At the 19 October 2026 raw prices the packs run from Makloee at £6.98 (3.7 from 11 reviews) to Faithfull FAICS300TP at £19.91, Faithfull Prestige at £28.49, and PRESCH or the Tracer kit at £34.99. Use £19.91 when you mean the amazon.co.uk capture for FAICS300TP.
PRESCH's short blade was measured by one reviewer at 152.4 mm, which is 6 in, even though the scales are metric. The Prestige rules are the light aluminium pair reviewers call flexible. The Tracer kit's two reviews do not tell you either head is square.
If you buy only one square
If the week's work is skirting and shelves, buy 300 mm. In this set that points at WORKPRO if you want the large review count. If the work is a pouch and small joinery, buy FAICS150. Buy a twin pack when you will do both in the same week, and flip-test each head before you cut. How those marks are drawn is on the how to use a combination square page. Which listing fits a metric workshop or a cast-iron head is on the best combination square page.
Common questions
Is 150 mm too small for skirting?
For a long skirting run, yes, a 150 mm blade is too short to be your only square. You can still mark a small return or a socket cut-out with it. Reviewers of Faithfull FAICS150 often say the square is smaller than they expected, which is the same limit. Use 300 mm when the board is long, and keep 150 mm for the joint.
Will 300 mm fit in a hinge recess?
A 300 mm square is awkward in a hinge recess because the head and the spare blade have nowhere to sit. The 150 mm square is the one that fits that pocket. You can force a long rule into the space and mark badly. Matching the blade to the recess is the simpler fix.
Is a twin pack two squares or one rule and two heads?
In this amazon.co.uk set, a twin pack is two squares: one 150 mm and one 300 mm, each with its own head. Faithfull FAICS300TP, PRESCH, flintronic, Prestige, Makloee and the Tracer kit are all sold that way. You flip-test both. A good small head does not certify the long one.
How much of a 300 mm rule can I actually mark with?
The head covers part of the blade, so the line you draw is shorter than 300 mm. Wirecutter's note on a 12 in rule is a bit over 10½ in of reach, about 267 mm, as their observation of that style of square. It is not a measured figure for every ASIN here. If you need a longer line, move the square and join the marks.
Which single square if I buy only one?
Buy 300 mm if the work in front of you is skirting, shelves or sheet layout. In this set, WORKPRO is the 300 mm listing with 4.7 from 5,203 reviews. Buy 150 mm if the work is a pouch and small joinery. Faithfull FAICS150 at £6.99 is that square. One length will feel wrong on the other job.
Do I flip-test both squares in a pack?
Yes. Lock each nut, mark from a straight edge, flip, and mark again. Parallel lines mean that head agrees with itself. A diverging pair means that square goes back, even if its partner was true. Do this before you cut, including on a set that arrived as one parcel.
Why do photos hide the size?
The listing image is cropped so a 150 mm square fills the frame the way a 300 mm square does. Faithfull's 150 mm reviews are full of people who expected a larger tool. Read the title in millimetres, and the weight if you want a second clue: FAICS150 is 99.8 g, while a 300 mm WORKPRO is 410 g.
Related pages
Sources
Sources taken from the research digest. Listings were captured on 19 October 2026.
- BSI, BS 939:2007 — engineers' squares (retrieved 20 October 2026)
- BSI, BS 4372:1968 — engineers' steel measuring rules (retrieved 20 October 2026)
- Measuring Instruments Regulations 2016, Schedule 1I (retrieved 20 October 2026)
- RS — combination squares (retrieved 20 October 2026)
- Cutwel — precision squares, angles and materials (retrieved 20 October 2026)
- BuildWiz — flip test for a builder's square (retrieved 20 October 2026)
- amazon.co.uk search — combination square (retrieved 20 October 2026)