Online Tool Store
Egg Timer Calculator
Calculate exact egg boil times by size, starting temperature, altitude, and doneness, then run a live countdown timer with an audio alert when it's done.
This works right here on your device — nothing gets sent out.
Recommended time
How it works
- Pick your egg size, starting temperature, desired doneness, and altitude (leave altitude at 0 for sea level) — the recommended time updates automatically.
- Bring a pot of water to a full boil, then lower the egg(s) in gently.
- Click Start timer the moment the egg goes into the water — the countdown locks in your settings so they can't drift out of sync mid-cook.
- When the timer ends, a chime plays (and a browser notification too, if you've turned that on) and the status line tells you it's time to plunge the eggs into cold water, which stops the cooking instantly.
- Click Reset to try a different size, temperature, doneness, or altitude.
The formula
This calculator uses the heat-conduction model published by physicist Charles Williams of the University of Exeter, which treats an egg as a homogeneous sphere and solves for the time it takes the centre of the yolk to reach a target temperature:
t = M^(2/3) · c · ρ^(1/3) / [K · π² · (4π/3)^(2/3)] · ln[0.76 · (T_egg − T_water) / (T_yolk − T_water)]
Where M is the egg's mass, c and ρ are the egg's specific heat capacity and density, K is its thermal conductivity, T_water is the boiling point of water at your altitude, T_egg is the starting temperature, and T_yolk is the target temperature at the centre of the yolk (about 65°C for soft-boiled and 77°C for hard-boiled). Example: a medium egg (57 g) straight from the fridge, boiled at sea level to a soft-boiled 65°C centre, works out to roughly 4 minutes 30 seconds — matching Williams' own published worked example.
FAQ
Why does egg size change the boil time so much?
Heat has to travel from the shell to the centre of the yolk, and a bigger egg means a longer path for that heat to travel — the calculator scales time with mass to the two-thirds power, so a jumbo egg needs noticeably longer than a small one for the same doneness.
Does starting temperature really matter?
Yes — a fridge-cold egg (about 4°C) starts further from its target yolk temperature than a room-temperature egg (about 21°C), so it needs more time in the water. Using the wrong starting temperature is one of the most common reasons a "perfect" recipe doesn't work at home.
Why does altitude affect the time?
Water boils at a lower temperature as altitude increases — about 95°C at 5,000 feet instead of 100°C at sea level. Cooler boiling water transfers heat more slowly, so eggs take longer to reach the same doneness. The calculator adjusts for this using your entered altitude.
Is this the same as starting eggs in cold water and bringing it to a boil?
No — this calculates time from the moment an egg is lowered into water that's already boiling, which is the method most competing calculators and this tool use because it's more precise (a cold-water start depends on your pot, stove, and quantity of water, none of which this tool can know).
What's the science behind the calculation?
It uses the heat-conduction model published by physicist Charles Williams (University of Exeter), which treats an egg as a sphere and solves for when the centre of the yolk reaches a target temperature — see "The formula" below for the full equation.
Does the timer keep running if I close this tab?
No — like any browser-based timer, it needs the tab open (in the background is fine) and your device awake. Nothing about your session is uploaded; the calculation and countdown both run locally in your browser.
How we compare
| Feature | Online Tool Store | Omni Calculator | egg-timer.org | alarmandclock.com |
|---|---|---|---|---|
| Live countdown timer with audio alert | ✓ | Calculator only — no running timer | ✓ | ✓ |
| Exact altitude-adjusted boiling point | ✓ | ✓ | Preset altitude bands only | Not available |
| Explains the underlying formula on the page | ✓ | Shows boiling point, not the full formula | Not shown | Not shown |
Omni Calculator's physics model is just as rigorous, but it stops at a number — you still need your own timer. egg-timer.org and alarmandclock.com give you a running timer but only rough altitude handling (or none at all). Egg Timer Calculator combines the precise, altitude-aware physics model with an actual countdown and alarm, in one page.