Buoyancy Calculator
Buoyant force from displaced volume in fresh or seawater.
What it does
Water pushes up on everything it surrounds with exactly the weight of the water moved aside. Two cubic meters of fresh water weigh 19,613.3 N, so anything displacing that volume feels precisely that lift. The tool above prices buoyancy from displaced volume in fresh or seawater.
The metric default floods 2 cubic meters fresh: 1000 kilos per cubic meter times 2 times 9.80665 is 19,613.3 N, about 4,409.2 lbf, from 2000 liters moved. Imperial mode floats 70 cubic feet of seawater for 4,479.2 lbf. Density picks the winner between otherwise equal hulls.
OpenStax college physics states the principle as force equals weight of fluid displaced and works a steel example where shape decides floating, while LibreTexts repeats the same law with the same steel numbers. Both stress the force exists whether objects float, sink, or hover.
Shape decides fate more than material does. A steel lump sinks while a steel hull floats because the hull displaces its own weight in water; the lump cannot. Load counts too: every added kilo needs another liter displaced to stay level.
How to use
- Pick metric (m3) or imperial (ft3).
- Type the displaced water volume.
- Pick fresh or seawater.
- Read buoyant force first.
- Compare against object weight to float or sink.
Formula
- V
- Displaced water volume.
- rho
- Water density by type.
- F
- Upward buoyant force.
Fully or partially submerged alike; only displaced volume counts. Apparent weight loss equals this force.
Worked example
Example: 2 m3 fresh water
Metric defaults: 2 m3, fresh.
- Mass: 1000 x 2 = 2000 kg displaced.
- Force: 2000 x 9.80665 = 19,613.3 N.
- Pounds: 19,613.3 x 0.224809 = 4,409.2 lbf.
- Volume: 2 m3 = 2000 L.
- Tool shows 19,613.3 N, 4,409.2 lbf, 2000 L.
Reference table
| Volume | Force | Pounds |
|---|---|---|
| 1 m3 | 9,806.7 N | 2,204.6 lbf |
| 2 m3 | 19,613.3 N | 4,409.2 lbf |
| 5 m3 | 49,033.3 N | 11,023.1 lbf |
| 10 m3 | 98,066.5 N | 22,046.2 lbf |
Limits
- Still water assumed; waves add dynamics.
- Rigid displacement; compressible hulls vary.
- Fresh and seawater only.
- Surface tension ignored.
Common mistakes
- Using object weight instead of displaced volume.
- Forgetting only submerged parts displace.
- Mixing fresh and seawater densities.
- Reading mass as force without g.
- Assuming shape never matters.
Try it yourself
Quick checks. Answers sit tucked under each question.
1 m3 fresh water?
1000 x 1 x 9.80665 = 9,806.7 N.
0.5 m3 seawater?
1025 x 0.5 x 9.80665 = 5,025.9 N.
70 ft3 seawater?
About 4,479.2 lbf of lift.
Questions
Buoyancy of 2 m3 fresh?
19,613.3 N upward.
Why do steel ships float?
Hulls displace their weight in water; lumps cannot.
Salt versus fresh?
Seawater at 1025 lifts about 2.5% more.
Apparent weight?
True weight minus buoyant force while submerged.
Partially submerged?
Only the wet volume counts.
Units here?
Newtons metric, pounds force imperial.