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Buoyancy calculator

Will it float or sink? Archimedes' principle: the buoyant force equals the weight of the displaced fluid, F = ρ·V·g. From the fluid density, the object's volume and mass, it computes the buoyant force, the weight, the net force, the object's density, the float/sink verdict and — if it floats — the fraction that sits below the surface.

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Need Buoyant force (N), Weight (N), Net force (N, + = up), Object density (kg/m³), Result, Fraction submerged (if floating)? The Buoyancy calculator derives it from Fluid density (kg/m³), Object volume, Volume unit, Object mass, Mass unit, Gravity (m/s²) in one step. For instance, with Fluid density (kg/m³) = 1,000, Object volume = 100, Volume unit = cm³, Object mass = 92, Mass unit = g and Gravity (m/s²) = 9.807 it returns Buoyant force (N) = 0.902, Weight (N) = 0.902 and Net force (N, + = up) = 0.078.

How to use it

  1. Enter your values: Fluid density (kg/m³), Object volume, Volume unit, Object mass, Mass unit, Gravity (m/s²).
  2. Read the result instantly: Buoyant force (N), Weight (N), Net force (N, + = up), Object density (kg/m³), Result, Fraction submerged (if floating).

Frequently asked questions

What does the Buoyancy calculator actually compute?

It takes Fluid density (kg/m³), Object volume, Volume unit, Object mass, Mass unit and Gravity (m/s²) and derives Buoyant force (N), Weight (N), Net force (N, + = up), Object density (kg/m³), Result and Fraction submerged (if floating) from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

6 values: Fluid density (kg/m³), Object volume, Volume unit, Object mass, Mass unit and Gravity (m/s²). Nothing else is required — no account, no file upload.

Can you show a worked example?

With Fluid density (kg/m³) = 1,000, Object volume = 100, Volume unit = cm³, Object mass = 92, Mass unit = g and Gravity (m/s²) = 9.807, the calculator returns Buoyant force (N) = 0.902, Weight (N) = 0.902 and Net force (N, + = up) = 0.078. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Fluid density (kg/m³) = 2,000, Object volume = 200, Volume unit = L, Object mass = 184, Mass unit = kg and Gravity (m/s²) = 19.61 instead, Buoyant force (N) goes from 0.902 to 3,608 — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Volume unit” option should I choose?

You can pick between « cm³ », « L », « m³ », « in³ » and « ft³ ». Each one changes what the calculator works out, so switch and compare — the default is « cm³ ».

What does it give for smaller values?

Scaled down to Fluid density (kg/m³) = 500, Object volume = 50, Volume unit = cm³, Object mass = 46, Mass unit = g and Gravity (m/s²) = 4.9, Buoyant force (N) comes out at 0.123. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.

What is the most common mistake?

Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.

What is the difference between the Buoyancy calculator and the Bernoulli equation calculator?

This one returns Buoyant force (N) and Weight (N); the Bernoulli equation calculator returns Solved value and Quantity (unit). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Falling through the Earth calculator (gravity tunnel) is the closest one after this: Jump into a frictionless tunnel bored through the Earth — how long to reach the other side? For a uniform Earth the motion is simple harmonic, so any straight chord takes the same ~42 minutes one way, with a peak speed of ~7.9 km/s through the centre. Switch to the PREM density model for the realistic ~38-minute figure.

Further reading

All guides →
ExplainerHow Buoyancy Works: Archimedes' Principle, and Why Ice Floats With 10.5 % Above WaterThe upward force equals the weight of the fluid pushed aside. That one sentence decides whether something floats, and if it floats, exactly how much of it stays under.ExplainerWhat Is the Reynolds Number? The Formula, the Units That Cancel, and Why 2 300 Is Only for PipesRe = ρvL/μ compares inertia with viscosity, and the units really do cancel. See the number worked out for honey, a household pipe, an artery, a swimmer and a wing — and why the 2 300 threshold belongs to pipe flow alone.ExplainerHooke's Law Explained: F = kx, Real Spring Constants, and Where It Stops HoldingHooke's law says force is proportional to stretch — but only below the elastic limit. Here is F = kx with worked numbers, what a 200 N/m spring actually feels like, and how springs combine.ExplainerHow the Doppler Effect Works: The Formula, the Sign Convention, and Why Moving the Source Is Not the Same as Moving the ListenerFor sound, f' = f(v + v_o)/(v − v_s) — and getting the signs backwards is the classic error. Here is the convention spelled out, a 440 Hz source computed at four speeds, and why light needs a different equation entirely.GuideThe Four Kinematics Equations: Which One to Use, and What Each One Leaves OutFive variables, four equations, and each equation is missing exactly one of them. Choose by looking at the variable the question never mentions.ExplainerProjectile Motion Explained: Range, Height, Flight Time — and Why 45° Is Not Always BestThree formulas cover the whole of projectile motion on level ground. The catch is level ground: the moment launch and landing heights differ, the 45° result stops being true.