Units guide
Metric and imperial units for material calculations
Keep linear, square, cubic and mass units distinct when measuring projects or comparing supplier quantities.
Length, area and volume
Length describes one dimension, area describes a surface and volume describes three-dimensional space. Their unit symbols change accordingly: m, m² and m³ are not interchangeable.
| Quantity | Metric examples | Imperial examples |
|---|---|---|
| Length | mm, cm, m | in, ft, yd |
| Area | m² | ft², yd² |
| Volume | L, m³ | ft³, yd³ |
| Mass | kg, metric tonne | lb, US short ton |
Exact linear relationships
| Relationship | Value |
|---|---|
| 1 m | 100 cm = 1,000 mm |
| 1 in | 25.4 mm |
| 1 ft | 12 in = 0.3048 m |
| 1 yd | 3 ft = 0.9144 m |
| 1 m³ | 1,000 L |
Why square and cubic conversions differ
A linear conversion factor is squared for area and cubed for volume. One yard is three feet, but one cubic yard is 3 × 3 × 3 = 27 cubic feet. Applying the linear factor only once produces the wrong result.
Mixed-unit example
A space is 12 ft long, 2.5 m wide and 75 mm deep. Twelve feet is exactly 3.6576 m and 75 mm is 0.075 m. Volume is 3.6576 × 2.5 × 0.075 = 0.6858 m³.
Shallow-depth errors
Entering 75 as metres instead of millimetres multiplies the intended depth by one thousand. Always check the selector adjacent to the input, especially for shallow landscape layers.
Ton versus tonne
A metric tonne equals 1,000 kg. A US short ton equals 2,000 lb. The words sound similar but are different mass units; conversions involving volume also require bulk density.
Practical checklist
- Write the unit beside every site measurement
- Check squared and cubed symbols
- Do not round converted dimensions before multiplying
- Confirm which ton a supplier means
- Keep density units compatible with mass and volume
Use the Cubic Metres Calculator, Cubic Yards Calculator, or review BulkMeasure methodology.
Square and cubic definitions
| Defined relationship | Area consequence | Volume consequence |
|---|---|---|
| 1 yd = 3 ft | 1 yd² = 9 ft² | 1 yd³ = 27 ft³ |
| 1 ft = 12 in | 1 ft² = 144 in² | 1 ft³ = 1,728 in³ |
| 1 m = 100 cm | 1 m² = 10,000 cm² | 1 m³ = 1,000,000 cm³ |
Volume-unit examples
A box 3 ft × 2 ft × 1.5 ft has volume 9 ft³. Dividing by 27 gives 0.333333 yd³. A metric space 2 m × 1.2 m × 0.25 m has volume 0.60 m³, equal to 600 L.
Mass units
Kilograms and pounds are mass units. A metric tonne is 1,000 kg; a US short ton is 2,000 lb. Neither can be converted to cubic metres or cubic yards without an applicable bulk density.
Density compatibility example
If density is supplied in kg/m³, use cubic metres to obtain kilograms. A hypothetical 0.75 m³ × 1,200 kg/m³ gives 900 kg. This example demonstrates unit compatibility and does not assert a material density.
Rounding and display
Exact defined conversion factors are retained through the calculation. Round only the displayed result. For example, 7 ft is exactly 2.1336 m; rounding it to 2.13 m before combining several dimensions introduces avoidable error.
Decimal feet and feet-and-inches
A decimal-foot value is not written in the same way as feet and inches. For example, 6.5 ft means 6 ft 6 in because 0.5 × 12 = 6. A written measurement of 6 ft 5 in equals 6 + 5 ÷ 12 = 6.416667 ft. Preserve the original notation and convert deliberately rather than typing the digits as a decimal.
Entry mistakes
- Entering 75 mm as 75 m
- Applying a linear conversion to square or cubic units
- Using a decimal foot value as feet and inches
- Confusing litres with cubic metres
- Leaving density units incompatible with volume
- Failing to identify short tons or metric tonnes
Continue with the Cubic Yards Calculator, Cubic Metres Calculator or the Volume & Weight Converters.