Trade toolkit · Setting out
Check whether a room, a frame or a carcass is square from its two diagonals, set out a right angle with the 3-4-5 method at any size, and solve any right-angled triangle from two values.
Check a room, floor or elevation for square
Measure two walls that meet at a corner, then both diagonals. Works the same for a wall elevation (width, height and diagonals) or a frame on the bench.
3-4-5 setting out
Mark 3 units along one line and 4 along the other. When the diagonal between the marks is exactly 5 units, the corner is 90°. Bigger triangles are more accurate, so use the biggest one that fits.
| Triangle | Short side | Long side | Diagonal | Fits? |
|---|
Right-angle triangle calculator
Type any two values, including at least one side. Rise and run work for stairs, ramps, roof pitches, scribes and braces.
How to use it
If a rectangle is square, its two diagonals are exactly the same length. If they are not, the room is a parallelogram and one corner is more than 90°. The Is the room square? tab takes the two wall lengths and both diagonals, then tells you the angle of the corner and how far out of square the far end of the wall is. That is the number you need when scribing a worktop or setting out a run of wall units.
A triangle with sides of 3, 4 and 5 units always has a right angle. Measure 3 along one line and 4 along the other, then adjust until the diagonal is exactly 5. The Set out a right angle tab scales this up to the biggest size that fits your space, for example 1800, 2400 and 3000 mm, because the bigger the triangle, the more accurate the right angle.
The Right-angle triangle tab works on Pythagoras (a² + b² = c²) and basic trigonometry. Fill in any two of rise, run, slope length or angle and it works out the rest, plus the gradient, the area and the perimeter. Use it for roof pitches, ramps, stair strings and sloping ceilings.
Questions
Measure both diagonals, corner to corner, at the same height. If they are the same, the room is square. If they differ, enter both diagonals and the two wall lengths here to get the actual corner angle and how much it is out over the length of the wall.
For kitchens and fitted furniture, a few millimetres over a wall is normal and is taken up by scribing. The tool flags anything over 3 mm and warns at over 10 mm, which is when you should plan scribe fillers or a wider worktop.
Any triangle with sides in the ratio 3:4:5 has a right angle between the two shorter sides. Builders and joiners use it to set out square corners on site with nothing but a tape measure: 300, 400 and 500 mm, or 1.2, 1.6 and 2.0 m, and so on.
More trade tools
Carpentry
Studs, plates, noggins, openings, timber lengths, plasterboard sheets and screws for a stud partition.
Kitchens
How many worktop lengths a kitchen needs, where the joints go and the cut length of every piece.
Carpentry
Number of steps, rise, going and pitch for a staircase, checked against UK Building Regulations.
Out of square walls?
Our made-to-measure cabinets and scribe panels are cut to your sizes, so odd corners and sloping ceilings are not a problem. Email info@dtjinteriors.co.uk, call 0115 784 8231 or WhatsApp 07956 032306.
DTJ Interiors Ltd
Unit 5 Atlas Mills, Birchwood Avenue
Long Eaton, NG10 3ND
Workshop and collection
Monday to Friday, 8am to 4:30pm
Delivery across the East Midlands for £99 + VAT, and further afield priced per job.
DTJ Interiors Limited · Company no. 15242186 · VAT GB460641310
Registered office: The Mills, Canal Street, Derby DE1 2RJ
Every DTJ cabinet comes with a 5-year guarantee. How it works · FAQs · Samples · Terms of sale
