Weight/Mass from Material + Volume
Finds the mass of a part, or of a tank’s contents, from its volume and the material’s density, and the weight that mass exerts under standard Earth gravity. Pick a metal, polymer, glass, ceramic, concrete or liquid to fill in its density, or type your own. Designers, estimators and riggers use it to price material, plan lifts and add up the loads on a structure.
Equations
m = ρ·V W = m·g0
m is the mass in kg, ρ the density and V the volume. W is the weight, the force of gravity on the mass, in newtons, and g0 = 9.80665 m/s² is standard gravity. The densities come from Callister for most solids [1], EN 1993-1-1 for steel [2], IAPWS-IF97 for water at temperatures from 5 °C up [3], Incropera for ethylene glycol, engine oil and mercury at 300 K [4], and CoolProp for ethanol and methanol [5]. A liquid’s name gives the temperature its density is for.
Limits and common mistakes
- Mass and weight are different things. A 10 kg part weighs 98.1 N. In pounds, 1 kg is 2.205 lb of mass, and it weighs 2.205 lbf.
- The listed densities are typical values. An alloy, a filled plastic or a concrete mix can differ by several percent, so use the supplier’s figure where the weight matters.
- Volume is the solid material only. Take out holes and pockets, and for a casting or weldment add the fillets and bosses. A CAD model’s volume is the easiest source.
- A liquid’s density changes with temperature. Water is 998.2 kg/m³ at 20 °C but 983.2 kg/m³ at 60 °C.
Worked example
A fixture needs a wrought aluminum plate 600 × 400 × 12 mm. How heavy is it, to choose the handling method?
- Choose Material Aluminum (wrought). The density fills in as 2700 kg/m³.
- Work out the volume: 600 × 400 × 12 = 2,880,000 mm³, or 2.88 L. Enter Volume 2.88 L.
- Press Solve. The Solution shows:
Mass: 7.776 kg
Weight (Earth gravity): 76.2565 N
Check: aluminum is about 2.7 kg per liter, and 2.7 × 2.88 = 7.78 kg, or 17.1 lb. The weight is 7.776 × 9.807 = 76.3 N. One person can lift the plate; the same plate in steel would weigh 22.6 kg.
