When two liquids have different densities, calculate each weight separately before adding them. Enter densities for the actual liquids and temperatures; use a measured final volume if mixing changes volume.

Formula: total lb = volume A × density A + volume B × density B; blend density = total lb ÷ final volume

Worked example

Five US gallons at 8.3 lb/US gal plus three at 7.2 lb/US gal weigh 41.5 + 21.6 = 63.1 lb. If the measured final volume is 8 US gal, the derived density is 7.8875 lb/US gal.

Mass is added component by component

NIST defines density as mass per volume. Use that relationship to calculate each liquid’s mass in pounds, then sum the masses. A single average of the two density numbers would be wrong when volumes differ.

A final volume may not be the sum

If measured final volume is blank, the calculator uses A + B volumes as an explicitly labeled approximation. Some mixtures contract or expand, so the derived density may be wrong even when component masses are correct. For an actual blend, measure its final volume and enter it.

Keep the physical basis matched

Both densities must use pounds per US gallon at relevant temperatures. This tool excludes container weight, reactions, evaporation and losses. Check compatibility and safe handling independently; the calculation does not recommend mixing substances.

Explore the related calculation

For a different starting point, try the liquid density measurement guide 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.

Found a problem? Email contact@gallonstopounds.org.

Liquid blend weight calculator

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