Egg Boiling Time Calculator
How long to boil an egg for a chosen yolk temperature, from its weight and starting temperature.
Results
What this tool does
Boiling an egg is a heat conduction problem, and it was solved properly: the time scales with the egg's weight to the two-thirds power, because that is how the surface area of a sphere relates to its mass, and it depends logarithmically on how far the yolk still has to travel in temperature. A large egg straight from the fridge needs roughly a minute and a half more than a small egg at room temperature — which is exactly the difference between a runny yolk and a set one.
Formula
t = 0.451 M^(2/3) ln[0.76 (T0 - Twater) / (Tyolk - Twater)]
Variables
| Symbol | Meaning | Unit |
|---|---|---|
mm | Weight of the egg | g |
t0 | Starting temperature | °C |
tw | Water temperature | °C |
ty | Target yolk temperature | °C |
TM | Boiling time | min |
TS | Boiling time | s |
MI | Whole minutes | min |
SE | Seconds | s |
Worked example
- Weight of the egg57 g
- Starting temperature4 °C
- Water temperature100 °C
- Target yolk temperature70 °C
- Boiling time5.94 min
- Boiling time356 s
- Whole minutes5 min
- Seconds56 s
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.
Frequently asked questions
What yolk temperature should I aim for?
About 63 °C for a barely set, spoonable yolk, 70 °C for the classic soft-boiled egg with a jammy centre, and 80 °C or more for fully hard-boiled. Egg white sets between 62 and 65 °C, so anything above that has a firm white regardless. The formula is Charles Williams' heat conduction model for a sphere, published at the University of Exeter, and it explains why a fridge-cold egg needs over a minute longer than a room-temperature one.