Boiled egg time calculator

How long to boil an egg depends on the yolk you want, the egg's weight and how cold it starts. A soft-boiled egg has a set white around a runny yolk, the dippy egg served with toast soldiers. A medium-boiled egg has a yolk set at the edge and soft in the middle, a jammy yolk, and a hard-boiled egg is firm right through. A large egg takes 5 minutes and 5 seconds to the soft stage.

Unless stated otherwise, every time below is for an egg from the fridge, lowered into water already boiling at sea level. A reading such as 4:35 means minutes and seconds, rounded to 5 seconds.

Egg size in the UK is a legal weight class. Commission Regulation (EC) No 589/2008, kept in Great Britain as assimilated law, sets four for class A eggs (Article 4), and Northern Ireland applies the EU's equivalent.

• Very large (XL): 73 g or more.
• Large (L): 63 g to under 73 g.
• Medium (M): 53 g to under 63 g.
• Small (S): under 53 g.

Boxes print the class beside the farming method, such as free-range. The calculator gives each class one egg weight, the middle of its band or just past an open end: 48 g, 58 g, 68 g and 78 g.

A typed weight from 5 g to 200 g makes it an egg boiling calculator by weight. An egg twice as heavy needs 1.59 times as long, not twice.

Quail eggs average about 11 g and duck eggs about 74 g (Poultry Science, 2019). The formula treats both like a hen's egg of another weight, so their different shells and yolks are not modelled.

A cold egg needs longer, because its centre has further to climb. A fridge egg starts at 4°C, as in Williams's own examples, and a room-temperature egg at 20°C, a convention rather than a measured figure.

For a medium egg, room temperature saves 1 minute and 15 seconds at every stage, because the starting temperature shifts the whole warming curve without changing its shape. A typed start from 0°C to 40°C covers anything in between.

The Food Standards Agency says that, ideally, eggs should be stored in the fridge (Home food fact checker). Temperature changes cause condensation, which it says lets more salmonella into the egg. UK supermarkets sell eggs unchilled, and boxes advise keeping them chilled after purchase.

Both are used in the UK, and they need different times. Williams's formula describes an egg lowered into water already at the boil, while a cold start also cooks the egg as the water heats.

The British Egg Information Service, run by the British Egg Industry Council, starts large eggs in cold water and times them from almost boiling. Its chart runs from 3 minutes for a really soft yolk to 8 minutes for firmly hard-boiled. Its own "Hot or cold water?" note still says the consensus points towards boiling the water first.

Those times leave out how cold the egg starts and how long the saucepan takes on the hob. For a fridge-cold large egg in a pan that boils after 5 minutes, the calculator gives 2:30, 4:05 and 8:45 after the boil.

No published model covers a cold start, so this is the calculator's own extension of Williams's formula, with the water warming steadily from 15°C. A soft medium egg then needs 2:00 after the boil, 7 minutes in all. A slower pan leaves less time after the boil, and a quail egg is soft before the water boils at all.

A gentle simmer below the boiling point is not modelled and cooks more slowly.

Water boils at a lower temperature as altitude rises, because the air pressure above the pan falls, and cooler water sets an egg more slowly.

At sea level the boiling point is 99.97°C, from the U.S. Standard Atmosphere 1976 for air pressure and the IAPWS-IF97 equation that the International Association for the Properties of Water and Steam publishes for water. On the summit of Ben Nevis, which the Ordnance Survey puts at 1,345 m, it falls to 95.5°C.

There a large one needs 40 seconds more to soft-boil and 2 minutes and 5 seconds more to hard-boil, as the 84°C target sits close to that lower boil. On Snowdon (Yr Wyddfa), 1,085 m high, water boils at 96.4°C. A kitchen 300 m up adds 10 seconds to that soft egg.

Williams notes that his formula under-predicts at altitude. Dr Edward Brooks found that an egg needing 3 minutes lower down took 5 minutes on Mount Washington in the United States, 1,917 m high. At that height the calculator adds only 50 seconds to a soft medium egg, so on a mountain the real time may run longer.

Dr Charles Williams, a physicist at the University of Exeter, published a formula for the time an egg needs in boiling water. It treats the egg as a uniform sphere heated from outside by conduction until the edge of the yolk reaches a chosen temperature.

The time grows with the egg's weight to the power of two thirds, times a logarithm comparing how far the egg and the target sit below the water temperature. Williams's constants are a density of 1.038 g/cm³, a thermal conductivity of 5.4 × 10⁻³ W/(cm K) and a specific heat of 3.7 J/(g K).

Protein coagulation decides each stage, so the target is the yolk temperature at its edge. Williams uses 63°C for a soft-boiled egg. Medium, 70°C, is the top of the range in which his page says yolk sets. Hard, 84°C, is where ovalbumin, the main protein of egg white, denatures (Foods, 2024).

No source defines medium or hard by a temperature, so those two are the calculator's own choices. A typed target from 55°C to 90°C replaces them. Williams's own rule for a hard egg, twice the soft time, gives 9:10 for a medium egg against 10:15 here.

His three examples, eggs of 47 g to 67 g, come out within 5 seconds of his figures, as checked against known answers shows. Cracked or very fresh eggs, steam ovens, egg cookers and microwaves fall outside the formula. The air fryer converter converts oven recipes, not eggs.

Each result carries a countdown set to the time shown, so it doubles as a kitchen timer. Its note says when to press Start: as the egg goes in, or when the water boils after a cold start.

At zero it plays three short tones and vibrates where the phone allows. While it runs, it asks the browser to keep the screen awake, which not every browser supports. Changing an input afterwards leaves it on its original time, with a note that the result has changed.

Lifting the egg out with a slotted spoon ends the boil but not the cooking. Heat already in the white keeps moving inwards, which cooks call carry-over cooking, and the formula leaves it out.

Williams plunges hard-boiled eggs into cold water, and the same industry service notes that it makes the egg contract slightly, so the shell is less likely to stick. An ice bath cools faster still, though no published model says by how much.

Eggs held hot for long, or cooled slowly, tend to show a green ring around the yolk.

The Food Standards Agency (FSA) says improved controls in the UK hen egg industry changed its advice on runny yolks. Young children, people who are pregnant, older people and people with an underlying health condition "can now safely eat raw or lightly cooked hen eggs".

That applies to eggs with a British Lion mark or from the Laid in Britain scheme, and not to people who are severely immunocompromised on medically supervised diets. The NHS adds that such eggs are less likely to contain salmonella.

For cooking in general, the FSA's test is the middle of the food reaching 70°C for 2 minutes (Cooking your food). The soft and medium stages stop short of it by design: their yolk-edge targets of 63°C and 70°C are reached only for a moment.