Area calculator
Calculate one rectangular area in square metres, keep the allowance visible and carry the result into a material-specific tool or supplier check.
20 LAUNCH TOOLS
Choose a calculator
When to use it
Use for one rectangle with straight sides and right-angled corners. For an L-shape or another irregular footprint, split the plan into non-overlapping rectangles and calculate each section separately.
How it works
Net area = length × width. Buying area = net area × (1 + waste ÷ 100).
Worked example
Assume a rectangular 5 m × 4 m surface and a 10% allowance. Net area = 5 × 4 = 20 m². Allowance = 20 × 0.10 = 2 m², so the buying area is 22 m² before checking the selected product's coverage and whole-pack increment.
Measurement guidance
Length and width in metres, plus a separate allowance percentage. Convert centimetres to metres by dividing by 100 and millimetres by dividing by 1,000.
Buying and specification checks
The result assumes a true rectangle measured in one plane. It is a planning calculation, not a surveyed measurement. Openings, slopes, pack coverage, coats, density and supplier sale increments are not inferred. The allowance is applied once and does not replace whole-pack rounding.
Measure and label the surface before choosing a product
The calculator handles rectangular geometry. Product coverage, layout, cutting, coats and ordering increments remain separate decisions.
- Sketch the boundary and label every dimension, opening and section. Use a suitable tape or laser measure, keep the units with each figure and repeat important measurements before ordering.
- For an L-shape, split the plan into rectangles that meet without overlapping. Calculate each net area, add the sections, then apply one justified allowance to the combined total rather than adding it twice.
- Keep surfaces separate: floor area is not wall area, and a sloping surface is not represented accurately by its horizontal plan measurement. Use the dimensions of the surface the product will actually cover.
- Check the selected product's stated coverage, number of coats, layout, pack size and sale increment. Round only at the correct final purchasing stage and retain the measured sketch with the order.
Common mistakes
- Mixing millimetres and metres
- Using floor area for wall coverage
- Rounding down before adding waste
FREE TOOL AND PROJECT PACK
What the free calculator provides
The free calculator gives the area of one rectangle and a separately stated allowance. It does not identify a paving system, optimise a layout, convert the result to packs or specify site preparation.
What the dedicated pack adds
If this area is for a patio or paved outdoor project, the Patio Project Pack adds project controls around the measurement.
- Measurement and site-readiness checklists.
- Quote comparison, ordering and delivery controls.
- Work-control, completion and retained project records.
19-page printable digital workbook (PDF). Immediate digital delivery with 90-day access; no subscription.
Practical FAQs
How do I calculate an L-shaped or irregular area?
Split it into non-overlapping rectangles, calculate each rectangle and add the net areas. Use the triangular-area calculator for triangular sections, then apply the chosen allowance once to the combined result.
How do I convert centimetres or millimetres to metres?
Divide centimetres by 100 or millimetres by 1,000 before entry. For example, 250 cm is 2.5 m and 4,000 mm is 4 m.
Should I subtract doors, windows or other openings?
Subtract only confirmed exclusions that the chosen product will not cover. Measure reveals, returns and other included surfaces separately so the same area is not missed or counted twice.
Does the result tell me how many packs or how much the material weighs?
No. It gives square metres with the allowance you entered. Use the selected product's coverage and whole-pack rule, or a material-specific calculator, and use a verified density if a weight conversion is needed.
Planning guidance, not a quotation or a substitute for project-specific design and competent advice.