When a filled container can be weighed, subtract its empty tare first. Divide the resulting liquid weight by a density for that same liquid and temperature, then compare it with the tank’s rated volume.

Formula: liquid lb = gross lb − tare lb; US gal = liquid lb ÷ (lb/US gal)

Worked example

A 1,550 lb gross reading minus a 350 lb tare is 1,200 lb of liquid. At a stated 8 lb/US gal, that is 150 US gal: 75% of a 200 US gal capacity.

Density is the missing conversion factor

A pound is mass and a US gallon is volume. Their ratio depends on the liquid and conditions. NIST defines density as mass divided by volume. Use a density measured or specified for the same liquid and temperature as the weighing, and keep its gallon convention aligned with this tool.

What a capacity comparison can tell you

The reported percentage is only estimated liquid volume divided by the capacity you entered. If the calculation exceeds that capacity, recheck gross and tare, liquid identity, density, units and the tank rating. The calculator flags the mismatch instead of treating it as a valid safe-fill instruction.

Scope of the estimate

Net weight can include residues or contents other than the intended liquid. Rated tank volume may differ from allowable working fill. No legal, pressure, thermal-expansion or transport limit is calculated here. To estimate the fill-line volume of an unknown container from repeated weighings, use the calibration worksheet.

Explore the related calculation

For a different starting point, try the container volume worksheet or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

www.nist.gov reference

Found a problem? Email contact@gallonstopounds.org.

Tank fill from weight calculator

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