Specific gravity calculator
Gives the specific gravity of a glycol mix and the feet of head per PSI (2.31 ÷ SG). Values are interpolated from published density tables.
How it works and source
SG = solution density ÷ 999.0 kg/m³ (water at 60 °F), so water at 60 °F reads 1.000 and 2.31 ft/PSI. Ft per PSI = 2.31 ÷ SG. The density is found by bilinear interpolation (concentration and temperature) in the table below. Cells left blank in the source are at or below the freezing point of that mix, and the page will not give a value there. Range: −49 to 212 °F.
Concentration is by mass (weight). Glycol suppliers often quote % by volume; for ethylene glycol the volume % is slightly lower than the mass % (about 28% vol ≈ 30% wt), and for propylene glycol they are nearly the same.
Source: densities of ethylene and propylene glycol water solutions from the ASHRAE Handbook—Fundamentals (glycol solution property tables), as tabulated by The Engineering ToolBox: ethylene glycol, propylene glycol (accessed Oct 2026). Check your inhibited fluid's data sheet (Dow, etc.) for exact figures; inhibitors add a little density.