What this converter does
The construction materials converter turns a weight of cement, sand, aggregate, steel or asphalt into the volume it occupies, and back again. Pick a material unit (in kilograms, or 50 kg cement bags) and a volume unit (cubic meters or cubic feet), enter a value, and press Convert. It divides weight by a fixed density, so the result is an estimate, not a measurement.
A pure unit conversion like meters to feet is exact. This one depends on how dense each material is assumed to be, and real materials don't all weigh the same.
Densities and units used
Every unit is converted through its volume. A kilogram unit's factor is 1 ÷ density, the volume one kilogram occupies, and the bag is 50 kg of cement at the same density.
| Unit in the list | Assumed density | 1 m³ equals | 1 unit equals |
|---|---|---|---|
| Cement (50kg bag) | 1,440 kg/m³ | 28.8 bags | 0.034722 m³ |
| Cement (kg) | 1,440 kg/m³ | 1,440 kg | 0.000694 m³ |
| Sand (kg) | 1,600 kg/m³ | 1,600 kg | 0.000625 m³ |
| Aggregate (kg) | 1,550 kg/m³ | 1,550 kg | 0.000645 m³ |
| Steel (kg) | 7,850 kg/m³ | 7,850 kg | 0.000127 m³ |
| Asphalt (kg) | 2,400 kg/m³ | 2,400 kg | 0.000417 m³ |
The two volume units are the cubic meter and the cubic foot (exactly 0.028316846592 m³, from NIST SP 811).
The cement, sand and aggregate figures are loose bulk densities: the weight of a cubic meter of the dry material as poured, air gaps included. Steel's 7,850 kg/m³ is the solid density of the metal, the same value behind standard rebar weight tables and this site's steel weight calculator. The asphalt figure, 2,400 kg/m³, is a typical value for compacted hot-mix asphalt, so it suits finished pavement better than loose material in a truck. The road asphalt calculator lets you change that density.
How much real materials vary
Density assumptions are where estimates go wrong, so check them against your supplier's data when the order is large.
- Sand changes volume with moisture. Damp sand bulks up and occupies more space than the same weight of dry sand, and saturated sand is heavier per cubic meter than dry sand.
- Aggregate density depends on the rock type and the mix of particle sizes. Well-graded stone packs more tightly than single-size stone.
- Cement packs down when vibrated or stored, so a settled bag weighs more per cubic meter than freshly poured powder.
- Asphalt is lighter loose than compacted, so a truck volume and a finished pavement volume aren't the same thing.
Worked examples
- Bags in one cubic meter of cement: 1 m³ = 28.8 bags.
- Volume of 10 bags: 10 × 50 ÷ 1,440 = 0.34722222 m³.
- One bag in cubic feet: 1.22620371 ft³.
- Space taken by a tonne of steel: 1,000 kg ÷ 7,850 = 0.12738854 m³.
- Sand for a 2.5 m³ heap: 2.5 × 1,600 = 4,000 kg, or 4 tonnes.
- Sand matched to cement by volume: for a 1:2 cement-to-sand mix measured by volume, one bag of cement needs two bags' worth of sand by volume. One bag converts to 55.56 sand kg, so that's about 111.1 kg of sand per bag of cement.
When to use a calculator instead
This converter is for quick weight-to-volume checks. To work out how much cement, sand and aggregate a whole job needs from its dimensions and mix ratio, use the concrete calculator or the brick calculator, which handle the dry-volume and wastage allowances. For plain unit conversions between liters, gallons and cubic yards, use the volume converter.
These figures are planning estimates. Confirm quantities with your engineer or supplier before ordering materials.
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