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Home and DIY Measuring Guides

Quick answer: For home and DIY jobs in the UK, measure in millimetres, take every dimension at least twice and in more than one place, and record the smallest figure for openings such as windows and doors. Standard UK sizes help: most internal doors are 1981 × 762 mm and plasterboard sheets are 2400 × 1200 mm.

This section collects step-by-step guides for measuring windows, doors, stairs, radiators, blinds, curtains and wallpaper, along with the standard sizes and calculations that save a second trip to the shop.

Why do UK trades measure in millimetres?

Millimetres avoid decimal points and the confusion between centimetres and metres. Kitchen fitters, window makers, joiners and builders’ merchants all quote sizes in millimetres, so a cupboard is 600 mm wide rather than 60 cm or 0.6 m. Ordering in the same unit as the supplier removes one conversion and one chance of error.

Imperial names still turn up in the trade. Sheet timber is often called “eight by four” (2440 × 1220 mm), older doors are described in feet and inches, and some timber is still known by inch sizes. When a product description mixes the two, trust the millimetre figure. The length conversions guide covers the exact factors if you need to translate an old plan.

What tools do you need for measuring at home?

  • A 5 m or 8 m steel tape measure with a sliding hook on the end, which moves by the thickness of the hook so inside and outside readings are both accurate.
  • A laser distance measure for room lengths and ceiling heights, where a tape would sag.
  • A spirit level and a square to check whether walls, sills and openings are true.
  • A pencil and notebook, with a quick sketch of the room or opening to write each figure on.

If you are unsure what the smaller marks mean, start with the guide on how to read a tape measure.

How do you measure a window or door opening?

Measure the width in three places and the height in three places, then use the smallest of each. Openings in real houses are rarely perfectly square, and a frame or blind made to the largest figure will not fit. The diagram shows the six measurements for a typical window opening.

Measuring a window opening in six placesA window opening with three width measurements at the top, middle and bottom and three height measurements at the left, centre and right, with example readings showing that the smallest width and height should be used.Measure three widths and three heightsW1W2W3H1H2H3WidthsW1 top: 1,210 mmW2 middle: 1,206 mmW3 bottom: 1,208 mmUse the smallest: 1,206 mmHeightsH1 left: 1,005 mmH2 centre: 1,002 mmH3 right: 1,004 mmUse the smallest: 1,002 mmExample readings, measuredinside the reveal, in mm
Example readings for a window opening: the smallest width and height are the safe figures to order from.
  1. Decide what you are measuring. For a replacement window or door, measure the structural opening brick to brick; for a blind inside the recess, measure inside the reveal; for curtains, measure the area you want to cover.
  2. Take three widths. Measure at the top, middle and bottom, and write each down.
  3. Take three heights. Measure at the left, centre and right.
  4. Check the diagonals. Measure corner to corner both ways. If the two figures are within a few millimetres, the opening is close to square.
  5. Use the smallest width and height. Makers then deduct their own fitting tolerance, so tell them whether your figures are the opening or the finished size.

What are the standard sizes in a UK home?

Many building products come in standard sizes, which makes planning and replacing them easier. The chart below lists common sizes in England and Wales; Scotland more often uses metric doors. Always measure the existing item, because older and period homes frequently differ.

ItemCommon UK sizeImperial equivalent
Internal door1981 × 762 × 35 mm6 ft 6 in × 2 ft 6 in
Other internal door widths610, 686 and 838 mm2 ft, 2 ft 3 in, 2 ft 9 in
Metric internal door2040 mm high, often 826 mm wideAbout 6 ft 8 in × 2 ft 8.5 in
External door1981 × 838 × 44 mm is common6 ft 6 in × 2 ft 9 in
Plasterboard sheet2400 × 1200 mm, often 12.5 mm thickAbout 7 ft 10 in × 3 ft 11 in
Plywood, MDF, OSB sheet2440 × 1220 mm8 ft × 4 ft
Standard brick215 × 102.5 × 65 mmAbout 8.5 × 4 × 2.5 in
Kitchen worktop depth600 mm (base units about 560 to 600 mm)About 2 ft
Wallpaper roll10.05 m × 0.53 mAbout 33 ft × 21 in

What do UK building regulations say about stair sizes?

In England, a private stair in a home can have a rise of up to 220 mm per step, a going of at least 220 mm and a pitch of no more than 42 degrees. These limits come from Approved Document K of the Building Regulations. They matter if you are replacing a staircase, converting a loft or checking whether an existing stair is steep.

MeasurementGuidance for a private stair
Rise (height of each step)Maximum 220 mm
Going (depth of each tread)Minimum 220 mm
Twice the rise plus the goingBetween 550 and 700 mm
PitchMaximum 42°
HeadroomAt least 2 m above the pitch line
Handrail height900 to 1000 mm above the pitch line
Gaps in balustradesA 100 mm sphere must not pass through

Rules differ in Scotland, Wales and Northern Ireland, and there are special provisions for loft conversions. Building work on stairs usually needs approval, so check with your local authority building control team or an approved inspector before you start. The staircase measuring guide shows how to take rise and going measurements.

How do you work out paint, flooring and wallpaper quantities?

Multiply length by width for floors, and perimeter by height for walls, then subtract doors and windows. Work in metres to get square metres directly. A room 4.2 m by 3.6 m has a floor area of 4.2 × 3.6 = 15.12 m². With a 2.4 m ceiling, the walls are (4.2 + 3.6) × 2 × 2.4 = 37.44 m²; taking away a 1981 × 762 mm door and a 1.2 m by 1.0 m window leaves about 34.7 m².

Paint tins state their coverage in square metres per litre, and two coats are usual. At 12 m² per litre, two coats on 34.7 m² need about 5.8 litres. For laminate and carpet, many fitters add 5 to 10 per cent for cutting waste. Wallpaper is counted in drops rather than area, which the wallpaper measuring guide explains.

What mistakes should you avoid when measuring for DIY?

  • Measuring only once. Walls, floors and openings are rarely true. Measure in several places and check your figures before ordering anything made to measure.
  • Copying the size of the old item. An old blind, radiator or door may never have fitted well. Measure the space, not the thing you are replacing, unless you need an exact like-for-like swap.
  • Forgetting obstructions. Window handles, sills, skirting boards, sockets and pipes all limit what fits. Note them on your sketch.
  • Mixing millimetres and centimetres. Write the unit beside every figure; 762 and 76.2 are easy to confuse later.

Home measuring guides in this section

Windows, doors and window dressing

Heating and stairs

Rooms, walls and fittings

Latest home and DIY measuring guides

    Related sections

    The units of measurement guide explains the metric system behind every plan. For floor areas and room sizes, see area and property measurement, and for pipes, cables and screws, see plumbing, electrical and hardware sizes.

    Frequently asked questions

    What is the standard internal door size in the UK?

    The most common internal door in England and Wales is 1981 × 762 × 35 mm, or 6 ft 6 in by 2 ft 6 in. Widths of 610, 686 and 838 mm are also standard, and metric doors are 2040 mm high.

    What size is a sheet of plasterboard?

    The standard UK plasterboard sheet is 2400 × 1200 mm, commonly 12.5 mm or 9.5 mm thick. Smaller 1800 × 900 mm sheets are easier to handle on your own.

    Should I measure a window inside or outside the frame?

    It depends on the job. For a replacement window, measure the brick opening around the frame; for a blind that fits inside the recess, measure inside the reveal; for curtains, measure beyond the frame to the area you want to cover.

    How do I check if an opening is square?

    Measure both diagonals from corner to corner. If they match within a few millimetres the opening is square; a bigger difference means the frame or fitting needs to allow for it.

    What is the maximum step height for stairs in a UK home?

    In England, Approved Document K allows a maximum rise of 220 mm per step for a private stair, with a going of at least 220 mm and a maximum pitch of 42 degrees.

    Sources