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.
Buoyancy Calculator on True Calculator gives you an instant, accurate answer with no sign-up and no app install. Calculate the buoyant force and apparent weight of an object submerged in water, seawater or oil using Archimedes' principle. Every result shows the formula and a worked example so you can verify the calculation yourself, and all values are computed in your own browser — your numbers never leave your device.
Popular uses: buoyancy calculator · buoyant force calculator · archimedes principle calculator
Reviewed by the True Calculator team · Last updated: August 2026
How We Calculate
This calculator uses standard physics and chemistry formulas verified by our team. All calculations are performed instantly in your browser using JavaScript — no data is sent to any server.
Formulas follow standard scientific definitions and physical constants, consistent with what is taught in school and university courses.
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.
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.
You might also need
Related calculators from other categories
Construction
BTU Calculator
Calculate the BTU and AC tonnage required for a room based on size, sun exposure and insulation.
Construction
Concrete Calculator
Calculate concrete volume, weight and number of cement bags for a slab. Get exact quantities for your construction project.
Construction
Gravel Calculator
Estimate gravel volume, weight in tonnes and 50 kg bags for driveways and paths by material density.
Construction
Mulch Calculator
Work out mulch volume in m³ and litres, plus bags needed and cost for your garden beds.