Construction Unit Conversion Table – Metric & Imperial Measurements

Quick construction conversion reference

Construction estimates often mix metric and US customary measurements. A drawing may show dimensions in millimetres, a product sheet may quote coverage in square feet, concrete may be ordered in cubic yards, and a material density may be listed in pounds per cubic foot. The safest approach is to convert each quantity within the same measurement type: length to length, area to area, volume to volume and mass to mass.

The factors below use standard unit relationships. For technical documentation, keep enough significant digits during the calculation and round the final result to match the precision of the original measurement.

Length conversion table: mm, cm, metres, inches, feet and yards

Length conversions are used before almost every construction quantity calculation. Convert dimensions first, then calculate area or volume. This avoids mixing metres with feet or millimetres with inches inside the same formula.

Converting feet and inches to metres

When a dimension is written as feet and inches, convert the inches to feet or convert both parts separately. For example, 8 ft 6 in equals 8.5 ft because 6 in = 0.5 ft. Then:

For site dimensions, keep the original measurement as well as the converted value. That makes it easier to check drawings and avoids silently replacing an exact project dimension with a rounded conversion.

Area conversion table: m², ft² and yd²

Area conversions matter for flooring, tile, drywall, roofing, decking, paving and paint coverage. A frequent mistake is to multiply square feet by 0.3048 because 1 ft = 0.3048 m. That is incorrect: area uses the square of the length conversion.

Example: convert 1,200 ft² to m²

A sensible displayed result may be 111.48 m² if the source area is known to that level of precision. For ordering flooring or tile, the next step is not another unit conversion: apply the project's waste allowance and round up to full boxes or packs.

Volume conversion table: m³, ft³, yd³ and litres

Volume is central to concrete, excavation, backfill, gravel and soil calculations. Because volume is three-dimensional, the conversion factor is the cube of the underlying length conversion. Small mistakes therefore become much larger than they do in a simple length conversion.

Example: cubic yards to cubic metres for concrete

A converted volume is still only a converted volume. If you are ordering concrete, aggregate or soil, use the relevant calculator to apply geometry, project allowance, density or package rounding rather than adding an arbitrary percentage during the unit conversion itself.

Weight conversion table: kg, lb, tonnes and short tons

Construction documents often use both metric tonnes (t) and US short tons. They are not the same unit. This matters when comparing aggregate deliveries, excavation haulage, steel weight or supplier pricing.

Density conversion: kg/m³ and lb/ft³

Density conversion is useful when the quantity is measured in one unit system and the supplier's bulk density is quoted in another. It is especially relevant to sand, gravel, crushed stone, soil, concrete and timber.

For example, a bulk density of 1,700 kg/m³ is approximately:

Density itself is not a universal fixed number for loose materials. Moisture, grading, voids and compaction can change bulk density, so use the Building Material Density Table as a planning reference and supplier or test data when accuracy matters.

Concrete pressure conversion: MPa, psi, kPa and bar

Concrete compressive strength and some construction equipment specifications are commonly expressed in MPa in metric documents and psi in US documents. Converting the number is useful for reading documents, but it does not prove that two concrete specifications are technically interchangeable.

Example: 4,000 psi to MPa

Use this as a unit conversion only. Concrete class designation, test method, age, exposure class and specification requirements must still be checked in the project documents.

Why square and cubic conversions use different factors

If 1 ft equals 0.3048 m, then a square foot is a square measuring 0.3048 m by 0.3048 m. Its area is therefore:

For volume, a cubic foot has three dimensions:

This is why using 0.3048 directly for square feet or cubic feet creates a major error. The same principle applies to inches, yards and every other squared or cubed length unit.

Practical examples for construction estimates

Flooring: 850 ft² to m²

Use 78.97 m² as the converted net area, then add the flooring waste allowance separately and round to complete boxes with the Flooring Calculator.

Concrete: 7.5 m³ to cubic yards

Use the Concrete Calculator for the actual order estimate because shape, project allowance and supplier ordering increments are separate from the unit conversion.

Excavated soil: 12 yd³ to m³

If this is excavated soil, distinguish in-situ excavation from loose spoil. The Excavation Calculator can apply a separate bulking assumption and compare truck volume with payload.

Aggregate density: 105 lb/ft³ to kg/m³

Use the converted density only if it describes the same product and material state as your estimate.

Common construction unit conversion mistakes