How do I measure a room for flooring?

Measure the longest length and the widest width of the room in metres. Multiply length × width for the floor area. For non-rectangular rooms, split into rectangles, calculate each area, and add them together. Always add 10% for waste when ordering flooring — more for patterned materials or diagonal laying.

How do I calculate wall area for painting?

Measure the perimeter of the room (total wall length) and multiply by the ceiling height. Then deduct the area of windows and doors — a standard door is approximately 1.98m × 0.76m (1.5m²) and a standard window is approximately 1.2m × 1.2m (1.44m²). The result is your net paintable wall area.

What is the difference between gross and net area?

Gross area is the total area including all openings (doors, windows, archways). Net area deducts these openings. For flooring, use the gross floor area (you need to cover the whole floor). For painting or tiling, use the net wall area (you do not paint doors and windows).

How do I measure an L-shaped room?

Split the L-shape into two rectangles. Measure each rectangle separately (length × width) and add the two areas together. It does not matter where you make the split — the total will be the same. For complex shapes, split into as many rectangles as needed.

Should I measure in metres or feet?

In the UK, most building materials are sold in metric units (m²). Measure in metres for consistency. If your tape measure only shows feet and inches, convert by dividing inches by 12 to get feet, then divide feet by 3.281 to get metres. Or simply use a metric tape measure.

How to Calculate Room Area — Step-by-Step UK Guide

What You'll Need

Tools

Tape measure (5m or 8m, metric)
Laser distance measurer (optional but very helpful)
Pen and paper or phone
Calculator

Tips for Accurate Measuring

Measure at floor level for flooring
Measure wall to wall, not skirting to skirting
Take two measurements and use the larger one
Measure in millimetres for precision, convert to metres
Sketch the room shape before measuring

Step-by-Step Instructions

Rectangular Rooms

Step 1: Measure the Length

Place the tape measure at one wall and extend it to the opposite wall. Measure at floor level, from wall to wall (not skirting board to skirting board — skirting boards add approximately 15-20mm on each side). Record the measurement in metres, e.g. 4.85m.

Step 2: Measure the Width

Measure the room at right angles to the first measurement. For rooms that are not perfectly square, take measurements at both ends and use the larger figure — this ensures you have enough material.

Step 3: Calculate the Floor Area

Multiply length × width. For example: 4.85m × 3.60m = 17.46m². This is the gross floor area.

L-Shaped Rooms

Step 4: Split into Rectangles

Sketch the room from above and divide the L-shape into two rectangles. Measure each rectangle separately. For example, an L-shaped room might split into a 4m × 3m section and a 2m × 2.5m section.

Step 5: Add the Areas

Calculate each rectangle: 4m × 3m = 12m² and 2m × 2.5m = 5m². Total floor area = 12 + 5 = 17m².

Bay Windows

Step 6: Measure the Bay

For a square bay window, measure it as an additional rectangle that projects beyond the main wall line. Measure the width of the bay opening and the depth of the projection. For an angled bay, approximate it as a triangle or trapezoid — measure the front width, back width and depth, then use the formula: area = (front + back) / 2 × depth.

Step 7: Add the Bay Area to the Room Area

Add the bay window floor area to the main room area. For example, a main room of 15m² with a bay of 1.5m² gives a total of 16.5m².

Calculating Wall Area

Step 8: Measure the Perimeter

Measure the length of each wall and add them together to get the perimeter. For a 4.85m × 3.60m room: perimeter = (4.85 + 3.60) × 2 = 16.9m.

Step 9: Measure the Ceiling Height

Measure from floor to ceiling. Standard UK ceiling heights are 2.4m (modern builds) or 2.6-3.0m (Victorian/Edwardian). Use the actual measurement, not an assumed figure.

Step 10: Calculate Gross Wall Area

Multiply perimeter × ceiling height. For example: 16.9m × 2.4m = 40.56m².

Step 11: Deduct Openings

Measure each window and door (height × width) and subtract from the gross wall area. Standard UK sizes: internal door ≈ 1.98m × 0.76m = 1.5m², standard window ≈ 1.2m × 1.2m = 1.44m², patio door ≈ 2.1m × 1.8m = 3.78m². Net wall area = 40.56 - 1.5 - (2 × 1.44) = 36.18m².

Quick Reference: Waste Allowances

Material	Waste Allowance
Carpet	5-10%
Laminate/engineered wood (straight lay)	10%
Laminate/engineered wood (diagonal lay)	15%
Vinyl/LVT	10%
Ceramic/porcelain tiles (straight lay)	10%
Ceramic/porcelain tiles (diagonal lay)	15%
Paint	10%
Wallpaper	15-20%

Common Mistakes to Avoid

Measuring skirting to skirting: Measure wall to wall at floor level. Skirting boards reduce the measured dimension by 30-40mm.
Forgetting alcoves and chimney breasts: Include alcoves on both sides of a chimney breast. Measure each alcove separately and add to the main area.
Not adding waste: Always add a waste allowance — cutting material generates offcuts that cannot be used. The more complex the room shape, the more waste.
Measuring once: Measure at least twice. Measure at both ends of the room if walls are not parallel — old houses are rarely perfectly square.
Confusing floor area and wall area: Floor area = length × width. Wall area = perimeter × height. They are very different numbers and used for different purposes.
Not sketching first: Draw the room shape before measuring. Label each dimension on the sketch. This prevents confusion when you get to the calculator.

Use our Room Area Calculator and Paint Coverage Calculator to work out areas and material quantities automatically.