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
| Field | What to enter |
|---|---|
| Egg length | Units: cm, mm, m, in, ft |
| Egg width | Units: cm, mm, m, in, ft |
| Egg mass | Units: g, kg, mg, lb, oz, gr |
| Salt in the bottom layer (g per litre) | A number |
| Top liquid density | Units: 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)
Formula
V_egg = (π/6)·L·W² (ellipsoid), ρ_egg = m/V, ρ_salt ≈ 998.2 + 0.73·c (c in g/L)
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.
Frequently asked questions
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.