[Symbiote]

Do most people know 62.4 lb/ft³?

The equivalent metric factor is 1 g/cm³ or 1 kg/L [1] so with D and H in centimeters the calculation is

  π D²/4 × H

kilograms of water.

[1] Assuming we're talking about a normal water tank, not a space rocket. Density varies with temperature, it's 0.9970474 g/cm³ at 25 °C.

[abduhl]

The unit weight of water being 62.4 pcf is probably not known by most people - most people don’t think in cubic feet. The more likely (and less useful) number most people know is ~8 lbs per gallon.