Buoyancy Calculator
What the Buoyancy Calculator does
Why does a steel ship float while a steel bolt sinks? The answer is buoyancy, the upward push every fluid exerts on a submerged object. Our Buoyancy Calculator delivers that force from just three inputs: Volume, Fluid density and Gravity.
Students use it to check physics homework, boat and kayak designers use it to size hulls, and divers and engineers use it to estimate lift bags, pontoons and tank buoyancy. Anyone deciding whether an object will sink or float qualifies as a user.
Archimedes' principle and a worked example
The tool applies Archimedes' principle, F = rho x g x V, where rho is the fluid density, g is gravity and V is the displaced volume. Fresh water has rho = 1000 kg/m3, and g is 9.81 m/s2 on Earth. The three inputs multiply directly, so scaling any one of them scales the force in equal proportion.
Picture a ball that displaces 0.002 m3 of water, about two liters. The force is 1000 x 9.81 x 0.002 = 19.62 N, roughly the weight of a 2 kg mass. In seawater at 1025 kg/m3 the same ball gains 20.1 N, slightly better lift.
How to use the calculator
Enter the submerged Volume first, in cubic meters for metric work. Next type the Fluid density: 1000 kg/m3 for fresh water, around 1025 for seawater, or 1.225 for air. The Gravity field defaults to 9.81 m/s2, but you can enter 1.62 for the Moon.
Press Calculate and read the upward force in newtons. Compare it against the object's weight to predict floating or sinking. Tip: for a floating hull, count only the part that sits below the waterline.
Frequently Asked Questions
What is the buoyancy formula in water?
F = rho x g x V. With water at 1000 kg/m3 and g at 9.81 m/s2, each cubic meter of displaced water produces 9810 newtons of upward force.
Why do heavy ships still float?
They are shaped to displace enormous volumes of water. A 100,000 tonne ship pushes aside more than 100,000 m3, so the total buoyant force balances its weight.
Does buoyancy change with depth?
No. For a fully submerged rigid object the force depends on displaced volume and fluid density, not depth. Pressure rises with depth, but its effect cancels out.
What gravity value should I enter?
Use 9.81 m/s2 on Earth, 1.62 on the Moon or 3.71 on Mars. Stronger gravity increases the buoyant force for the same displaced volume.
Is buoyancy stronger in saltwater?
Yes. Saltwater density is about 1025 kg/m3 versus 1000 for fresh water, so the same submerged object gains roughly 2.5 percent more lift.