Buoyancy Calculator
Calculate the buoyant force and apparent weight of an object submerged in water, seawater or oil using Archimedes' principle.
Optional — used to find the apparent weight in the fluid.
Buoyant force
98.07 N
Displaces 10 kg of fluid
Apparent weight
392.27 N
Weight in the fluid, not in air
Buoyant force = fluid density × displaced volume × gravity (g = 9.80665 m/s²). An object floats when buoyancy exceeds its weight.
Last updated: August 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Buoyancy decides whether things float, and India relies on it daily: fishing boats on the Bay of Bengal, ferries on the Ganga, and the hull design of naval ships all follow Archimedes' principle. A lactometer floats higher in purer milk because density changes the upthrust, and lifeguards teach that salt water supports swimmers more than pool water. Underwater construction workers and scuba divers use the same force balance to adjust ballast weights. When you need the upthrust on a submerged object — a water tank test, a well casing, or a physics practical — this calculator gives the force and the apparent weight instantly.
How to Use This Calculator
- Step 1: Choose the fluid — fresh water, seawater or oil.
- Step 2: Enter the volume of the object that is submerged, in litres.
- Step 3: Enter the object's weight in air, in kg, if you want the apparent weight.
- Step 4: Read the buoyant force in newtons, the fluid displaced in kg, and the apparent weight in the fluid.
Worked Example
A 10 kg stone lowered into a bucket displaces 2 litres of water. Water gives an upthrust of 2 × 9.80665 = 19.61 N, so the stone's apparent weight in water is 10 × 9.80665 − 19.61 = 78.45 N instead of 98.07 N — it feels about 2 kg lighter. In seawater, the same 10 litres displaced pushes up with 1025 × 0.01 × 9.80665 = 100.52 N because seawater is denser at 1,025 kg/m³, which is why swimmers float slightly higher at the beach than in a pool.
Tips and Common Mistakes
- •Tip 1: Use only the submerged volume — a floating object displaces less than its full volume.
- •Tip 2: If the apparent weight comes out negative, the object will rise to the surface.
- •Tip 3: For boats, the displaced mass equals the load they can carry — 1 litre of water displaced supports 1 kg in fresh water.
- ✗Mistake 1: Entering the object's full volume when only part of it is under water.
- ✗Mistake 2: Using litres where the formula expects cubic metres — the calculator handles the conversion for you.
Sources and References
- •Archimedes' Principle — University Physics (Young & Freedman)
- •NCERT Class 11 Physics, Chapter 10: Mechanical Properties of Fluids
- •Fluid densities at standard conditions — CRC Handbook of Chemistry and Physics
Official sources are linked so you can confirm the current rate yourself. Check the linked page for the latest notification before relying on these figures.
Frequently Asked Questions
What is the buoyant force formula?
Buoyant force = fluid density × displaced volume × gravity, with g = 9.80665 m/s². Submerging 1 litre in fresh water displaces 1 kg and creates about 9.81 N of upthrust.
Why do objects feel lighter in water?
The water pushes up with a force equal to the weight of the fluid displaced. Subtract that upthrust from the object's real weight and you get its apparent weight in the fluid.
When does an object float?
When the buoyant force equals or exceeds the object's weight. If the apparent weight is negative, the object rises to the surface and floats with part of its volume above water.
How is buoyancy used in India?
Dredging, boat capacity limits, submarine ballast tanks and even checking the density of milk with a lactometer all rely on Archimedes' principle, which this calculator demonstrates.
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