Egg timer
Pick the size and the yolk you want. The time adjusts for eggs straight from the fridge and for altitude, then rings when it’s time for the cold water.
Boil for 7:00, then straight into cold water.
Alarm & notification settings
Sound needs one tap on the page first (a browser rule). Keep this tab open: closing it stops every timer’s alarm. Why timers stay accurate in background tabs.
Why a bigger or colder egg needs longer
An egg cooks from the outside in. The white starts to set at about 62–65°C and turns firm by around 80°C; the yolk thickens from about 65°C and is fully set near 70°C and above. Heat reaches the middle last, so the time is really about how long the centre takes to catch up.
Charles Williams, a physicist at the University of Exeter, wrote this as a formula: time grows with the egg’s mass to the power of two-thirds, times the logarithm of how far the egg has to warm compared with how far the yolk is from the water temperature. That is why a jumbo egg needs about 16% longer than a large one, a fridge-cold egg needs longer than a room-temperature one, and a lower boiling point at altitude slows everything down.
Our times start from widely used kitchen timings for a large egg and scale them with Williams’ relation, so treat them as a very good first guess and adjust a little for your pot.
- White: fully set
- Yolk: thickening at the edge, runny centre
A simplified picture of the heat moving inwards, for the settings above.
Questions
How long do you boil an egg?
For a large egg straight from the fridge lowered into boiling water at sea level: about 6 minutes for a runny yolk, 7 for jammy, 8½ for a softly set yolk and 11 for hard-boiled. Then move it to cold water to stop the cooking.
Do eggs take longer at high altitude?
Yes. Water boils at a lower temperature as you go up, roughly 1°C lower for every 300 m (about 1°F per 500 ft), so the egg heats more slowly. The calculator adjusts for altitude.
Should I start eggs in cold or boiling water?
These times are for eggs lowered into water that is already at a rolling boil, which is more repeatable because you know exactly when cooking starts. Starting in cold water depends on your pot and stove.
Why does the egg size matter so much?
Heat has to travel from the shell to the centre. In the physicist Charles Williams’ egg formula, cooking time scales with the egg’s mass to the power of two-thirds, so a jumbo egg needs noticeably longer than a medium one.