Density Calculator · Practical guide
What Is the Density of Water in lb per Cubic Foot?
Water weighs 62.428 lb/ft3 at its densest — the number behind everything from aquarium stands to pool load calculations.
At a glance
Quick answer
The density of water is 62.428 pounds per cubic foot (usually rounded to 62.4 lb/ft³) at around 4 °C, where it is densest. In metric units that same density is 1,000 kg/m³ or exactly 1 g/cm³.
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The Conversion
Starting from the metric standard of 1,000 kg/m³, multiply by the exact factor 0.062428 to get 62.428 lb/ft³. Working the other direction, multiply lb/ft³ by 16.0185 to recover kg/m³. The calculator above applies this factor automatically, so entering 1,000 kg and 1 m³ shows 62.428 lb/ft³ alongside the metric values.
Densities of Common Liquids
| Liquid | kg/m³ | lb/ft³ |
|---|---|---|
| Gasoline | 750 | 46.8 |
| Fresh water (4 °C) | 1,000 | 62.4 |
| Seawater | 1,025 | 64.0 |
Why the Number Matters
- A 55-gallon aquarium holds about 7.35 ft³ of water — over 458 lb before the glass and gravel.
- Hot tub and pool structural loads are calculated directly from 62.4 lb/ft³.
- Ice floats because it expands to about 57.2 lb/ft³, roughly 8% lighter than liquid water.
Does Temperature Change It?
Yes, slightly. Water is densest near 4 °C; at room temperature it is closer to 62.3 lb/ft³, and near boiling it drops below 60. For everyday estimates, 62.4 lb/ft³ is the value to use.
Frequently Asked Questions
How much does one cubic foot of water weigh?
About 62.4 pounds at cool temperatures. Since a cubic foot is 7.48 US gallons, one gallon of water weighs roughly 8.34 pounds.
Is seawater denser than fresh water?
Yes. Dissolved salt raises seawater's density to about 1,025 kg/m3, or 64.0 lb/ft3 — roughly 2.5% heavier than fresh water, which is why floating is easier in the ocean.
Why is water densest at 4 degrees Celsius?
Water molecules form a more open crystal structure as they approach freezing, so water expands both when heated above 4 °C and when cooled below it. That quirk is why ice floats.
How do I convert lb/ft3 back to kg/m3?
Divide by 0.062428, or multiply by 16.0185. For example, 62.428 lb/ft3 converts back to exactly 1,000 kg/m3.