BuildCalcs Square metres: area
Length × width gives area. A floor 4 m × 3 m is 12 m². Area is appropriate for surfaces such as flooring, paintable walls, insulation coverage and paving footprints.
Cubic metres: volume
Length × width × depth gives volume. If that 12 m² floor receives a 100 mm layer, first convert 100 mm to 0.10 m. Then 12 × 0.10 = 1.20 m³.
Useful depth conversions
| Millimetres | Metres |
|---|---|
| 1 mm | 0.001 m |
| 10 mm | 0.01 m |
| 25 mm | 0.025 m |
| 50 mm | 0.05 m |
| 75 mm | 0.075 m |
| 100 mm | 0.10 m |
| 125 mm | 0.125 m |
| 150 mm | 0.15 m |
| 200 mm | 0.20 m |
A quick dimensional check
If you are estimating concrete, screed, sand or aggregate and your final result is only in m², you probably have not yet included depth. If you are estimating paint or sheet coverage and your result is in m³, you may be solving the wrong quantity.
Worked multi-step example
A path is 8 m long × 1.2 m wide: area = 9.6 m². A 75 mm layer is 0.075 m. Volume = 9.6 × 0.075 = 0.72 m³. If a separate product conversion is needed, it should be applied only after this volume is established.
Why unit consistency matters
Multiplying 8 × 1.2 × 75 without converting the 75 mm depth would produce 720, a number with mixed units that is not 720 m³. Converting all dimensions to metres before a cubic-metre calculation prevents this common thousand-fold error.
Enter your actual measurements rather than relying on a generic example.
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