Egg Boiling Calculator
Enter your egg size, starting temperature, and altitude to get precise boiling times for soft, medium, and hard boiled eggs. The calculator uses a physics-based heat-diffusion formula that accounts for how altitude lowers the boiling point of water, so your results are accurate whether you are cooking at sea level or high in the mountains.
The physics of boiling an egg
The time it takes to boil an egg is governed by heat diffusion through a roughly spherical object. The widely cited formula, published by physicist Charles Williams, treats the egg as a sphere with a known mass, density, specific heat capacity, and thermal conductivity. Heat flows from the boiling water inward, and the formula calculates how long it takes the center (the yolk) to reach a target temperature. The key insight is that egg size matters more than most people expect: a jumbo egg needs nearly twice as long as a peewee at the same doneness, because heat must travel further to the center.
How altitude changes your boiling time
Water boils at 100 C at sea level, but at higher altitudes the atmospheric pressure is lower and water boils at a lower temperature. At 1000 m elevation, water boils at about 96.5 C. At 3000 m (roughly the altitude of many Andean cities) it boils at only 89.5 C. Because the water is cooler, heat transfers to the egg more slowly, and the egg takes longer to reach the target internal temperature. This calculator automatically adjusts for your altitude using a standard barometric pressure model: roughly 0.35 C lower boiling point per 100 m gained, adding about 20-30 seconds per 500 m for a standard large egg.
Fridge eggs vs room-temperature eggs
Starting temperature has a significant effect on boiling time. A large egg fresh from the fridge (4 C) takes about 1 minute longer than the same egg at room temperature (20 C) to reach the same internal temperature. Fridge eggs also crack more easily when they hit boiling water due to the sudden thermal shock; a 30-second immersion in warm tap water before boiling, or lowering the egg gently on a spoon, helps prevent this. For the most consistent results, use the same starting condition every time you cook.
Getting the perfect doneness every time
This calculator targets three precise internal temperatures: 63 C for soft (whites just set, yolk still runny and bright), 68 C for medium (whites fully firm, yolk creamy and jammy), and 77 C for hard (both white and yolk fully set, no greenish ring). The greenish-grey ring that sometimes appears on hard boiled eggs is a harmless iron-sulfur compound that forms when the yolk overheats above about 82 C. Stopping at 77 C avoids this entirely. After boiling, transfer the egg to an ice bath immediately to stop carry-over cooking, which can push the internal temperature up by 2-3 C after the egg leaves the water.
Egg boiling times at sea level
| Size | Mass | Soft (fridge) | Soft (room) | Medium (fridge) | Hard (fridge) |
|---|---|---|---|---|---|
| Peewee | 38 g | 4 min 30 sec | 3 min 45 sec | 5 min 15 sec | 7 min 30 sec |
| Small | 45 g | 5 min 0 sec | 4 min 10 sec | 5 min 50 sec | 8 min 20 sec |
| Medium | 53 g | 5 min 30 sec | 4 min 40 sec | 6 min 30 sec | 9 min 10 sec |
| Large | 60 g | 6 min 0 sec | 5 min 0 sec | 7 min 0 sec | 10 min 0 sec |
| Extra Large | 68 g | 6 min 30 sec | 5 min 30 sec | 7 min 30 sec | 10 min 45 sec |
| Jumbo | 78 g | 7 min 15 sec | 6 min 0 sec | 8 min 20 sec | 11 min 45 sec |
Times assume the egg is placed in already-boiling water (100 C). Fridge start = 4 C; room temp = 20 C.
Frequently asked questions
Do I start the timer when I put the egg in the water, or when the water comes to a boil?
Start the timer the moment the egg goes into water that is already at a full, rolling boil. If you add the egg to cold water and heat together, the timing is much harder to control and depends on your stove and pot size. The times in this calculator assume you are using the "hot start" method: boil the water first, then add the egg.
Why does altitude make eggs take longer to boil?
At higher altitude, atmospheric pressure is lower. Water evaporates more easily at lower pressure, so it boils at a lower temperature. At 2000 m, water boils at about 93 C instead of 100 C. Because the temperature difference between the water and the egg is smaller, heat transfers more slowly, and the egg takes longer to reach the same internal temperature. For every 500 m of altitude, add roughly 30-40 seconds to a standard large egg.
How do I stop a hard boiled egg from getting a greenish yolk?
The green-grey ring forms when the yolk overheats above about 82 C, causing iron in the yolk to react with hydrogen sulfide from the white to form ferrous sulfide. To prevent it, stop cooking at 77 C (which this calculator uses as the hard boiled target) and transfer the egg to ice water immediately after boiling. Do not overcook, and do not leave hard boiled eggs in hot water to cool.
Can I put cold eggs straight from the fridge into boiling water?
Yes, but lower them in gently with a spoon rather than dropping them. Cold eggs are more prone to cracking from thermal shock. An alternative is to place them in cold water, bring it to a boil, then remove the pot from heat and let the eggs sit covered for the time this calculator recommends for your chosen doneness (adding about 1 minute to compensate for the heating-up phase). The calculator uses the "hot start" method, which gives more consistent and controllable results.
Does the formula work for quail eggs or duck eggs?
The formula assumes the thermal properties of a standard chicken egg. Quail eggs weigh about 9-12 g, so entering a custom weight of 10 g will give a reasonable estimate. Duck eggs weigh 60-90 g and have a slightly thicker shell but similar internal properties, so the formula is still a good approximation when you enter the actual weight. For very large eggs, use the custom weight input.
My eggs keep cracking. What can I do?
Cracking usually happens from thermal shock (cold egg hitting boiling water) or air expanding inside the shell too rapidly. Fixes: lower eggs in on a spoon, use room-temperature eggs, prick the wide end with a pin to release the air pocket before boiling, and use a pot large enough that the eggs are not banging against each other. Adding a teaspoon of salt or vinegar to the water does not prevent cracking but does help seal hairline cracks if they do occur.