# Buoyancy Experiment Calculator (Floating Egg)

URL: https://speedycalculator.com/calculators/physics/buoyancy-experiment/
Last updated: 2026-10-30

> The floating egg calculator predicts whether an egg sinks, floats or hovers between a layer of salty water and fresh water, from the egg's size and mass and the salt concentration.

## Inputs

- Egg length (cm, mm, m, in, ft)
- Egg width (cm, mm, m, in, ft)
- Egg mass (g, kg, mg, lb, oz, gr)
- Salt in the bottom layer (g per litre)
- Top liquid density (kg/m³, g/cm³, g/mL, lb/ft³, lb/in³)

## Results

- Egg volume
- Egg density
- Bottom (salt water) density
- The egg
- Salt needed to float the egg

## Formula

```
V_egg = (π/6)·L·W² (ellipsoid),  ρ_egg = m/V,  ρ_salt ≈ 998.2 + 0.73·c (c in g/L)
```

## Explanation

A fresh egg sinks in tap water but floats in strong salt water. Carefully pour fresh water over salty water and the egg hangs in the middle – a classic kitchen demonstration of density and buoyancy.

### How to use the Buoyancy Experiment Calculator

- **Egg length**
- **Egg width**
- **Egg mass**
- **Salt in the bottom layer (g per litre)**
- **Top liquid density**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the egg's length, width and mass, the salt concentration of the bottom layer and the density of the top layer.

### Inputs explained

FieldWhat to enterEgg lengthUnits: cm, mm, m, in, ftEgg widthUnits: cm, mm, m, in, ftEgg massUnits: g, kg, mg, lb, oz, grSalt in the bottom layer (g per litre)A numberTop liquid densityUnits: kg/m³, g/cm³, g/mL, lb/ft³, lb/in³

### What each result means

- **Egg volume** = pi÷6×[Egg length]×[Egg width]^2×1e6
- **Egg density** = [Egg mass]÷(pi÷6×[Egg length]×[Egg width]^2)
- **Bottom (salt water) density** = 998.2 + 0.73×[Salt in the bottom layer (g per litre)]
- **Salt needed to float the egg** = max(0, ([Egg density] - 998.2)÷0.73)

## Worked example

Inputs — Egg length: 5.7 cm; Egg width: 4.4 cm; Egg mass: 60 g; Salt in the bottom layer (g per litre): 100; Top liquid density: 998.2 kg/m³.

Results — Egg volume = 57.7802 cm³; Egg density = 1,038.41851 kg/m³; Bottom (salt water) density = 1,071.2 kg/m³; **The egg = Hovers at the boundary between the layers**; Salt needed to float the egg = 55.1 g/L.

## Key terms

- **Density**: Mass per volume.

## FAQ

**Why do eggs float in salt water?**
Dissolved salt makes the water denser than the egg.

**Why does an old egg float even in tap water?**
Its air cell grows as moisture escapes, lowering its density.

**How do I make the layers?**
Pour fresh water slowly over the back of a spoon onto the salty layer.

**How much salt do I need?**
Usually 60–100 g per litre for a fresh egg.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)