Convert a material quantity between volume and mass using an explicit density. Both directions share one page, including gallons to pounds, cubic yards to tons and liters to kilograms.
Choose units and the material condition
Select Volume to weight when you know a container or loose-material volume. Select Weight to volume for a measured mass. Choose both unit definitions, then a material example or Custom / supplier density. The result shows the density actually used so a hidden material assumption cannot change your answer unnoticed.
For a custom density, enter its number and unit together. A density of 1 kg/L is the same as 1,000 kg/m³. In a preset calculation the custom-density fields are ignored. If mass and volume are both known and density is unknown, use the Density Calculator.
Gallons and tons need their full names
US liquid gallons and imperial gallons differ in size. Likewise, a metric tonne is 1,000 kg, a US short ton is 2,000 lb and an imperial long ton is 2,240 lb. The unit menus label all three. Fluid ounces are volumes; ordinary and troy ounces are masses. Changing density is essential when crossing from one quantity to the other.
Water and bulk-material estimates
The water preset uses an approximate fresh-water density of 998.2 kg/m³ near 20°C. It is not a temperature-dependent model and does not describe seawater. Use measured density when temperature, dissolved material or pressure matters.
The construction examples reuse the existing planning-tool densities, labeled with their assumed pounds per cubic foot. They are illustrative values, not certified material properties. Loose gravel, wet soil and compacted fills can have different bulk densities. Use supplier data for the actual product and condition. The converter adds no waste, compaction or delivery allowance; the Cubic Yard Calculator handles project quantities and ordering allowances.
USGS discusses how water density varies with conditions.
Formula
mass in kg = volume in m³ × density in kg/m³
volume in m³ = mass in kg ÷ density in kg/m³
1 US liquid gallon = 0.003785411784 m³
1 cubic yard = 0.764554857984 m³
Examples
Fresh water in a US gallon
At the stated 998.2 kg/m³ density, 1 US gallon contains approximately 3.778598043 kg of water. This excludes the container.
A supplier density
At a custom bulk density of 1,600 kg/m³, 2 m³ has a mass of 3,200 kg, or 3.2 metric tonnes. Reversing 3.2 tonnes gives 2 m³.
Precision and definitions
Calculations retain unrounded values internally. Displayed digits do not increase the accuracy of measurements. NIST unit definitions provide the conversion reference.