What this calculator does
Boiling times are published for large eggs, and other sizes need adjusting. The scaling is not proportional to weight: heat has to conduct inward from the surface, so time scales with mass to the power of two thirds, which is the surface-area-to-volume relationship.
The effect is real but modest. A jumbo egg at 71 g takes 10 minutes 25 seconds where a large egg takes 9 minutes, and a small egg takes 7 minutes 27 seconds. That is a three minute spread across the size range, which is easily enough to be the difference between a jammy yolk and a chalky one.
The formula
The baseline time for a large egg at the chosen doneness is multiplied by the egg mass divided by 57 g, raised to the power of two thirds. The two-thirds exponent comes from the geometry: volume scales with the cube of a linear dimension while surface area scales with the square, so the time for heat to reach the centre scales with the ratio between them. Times assume the egg is added to already-boiling water.
| Term | Meaning |
|---|---|
| Two-thirds scaling | The exponent relating cooking time to mass, from the surface-area-to-volume relationship. |
| Soft-boiled | Around 6 minutes for a large egg, giving a runny yolk. |
| Jammy | Around 9 minutes, giving a set white and a soft, spreadable yolk. |
| Hard-boiled | Around 12 minutes, fully set throughout. |
The inputs explained
| Field | What to enter |
|---|---|
| Egg size (USDA) | Egg size, which sets the mass used in the scaling. |
| Doneness | How done you want it, which sets the baseline time for a large egg. |
When to use it
Cooking eggs of an unfamiliar size
Farm eggs and mixed boxes vary considerably, and the published time assumes large. The adjustment is what stops a jumbo egg coming out underdone.
Hitting a jammy yolk reliably
The window between runny and set is narrow, on the order of a minute or two, which is exactly the range that egg size shifts things by.
Scaling a batch
The time is per egg regardless of how many are in the pan, though a crowded pan drops the water temperature when the eggs go in and needs a moment to return to the boil.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does egg size change the boiling time?
The five standard egg sizes at the same doneness setting.
| Egg size | Boiling time | In minutes | Baseline used |
|---|---|---|---|
| Small (43 g) | 7:27 | 7.46 min | Large egg (57 g), added to already-boiling water |
| Medium (50 g) | 8:15 | 8.25 min | Large egg (57 g), added to already-boiling water |
| Large (57 g) | 9:00 | 9.00 min | Large egg (57 g), added to already-boiling water |
| Extra large (64 g) | 9:43 | 9.72 min | Large egg (57 g), added to already-boiling water |
| Jumbo (71 g) | 10:25 | 10.42 min | Large egg (57 g), added to already-boiling water |
Questions
How long to boil an egg?
For a large egg added to already-boiling water: about 6 minutes for a runny yolk, 9 for jammy and 12 for fully hard-boiled. Other sizes need adjusting, and starting from cold water changes everything since the timing then includes bringing the water up.
Why does time scale with the two-thirds power?
Because heat enters through the surface and has to reach the centre. Surface area scales with the square of a linear dimension and volume with the cube, so the time to heat through scales with the ratio, which works out as mass to the power of two thirds rather than to the power of one.
Should I start in cold or boiling water?
These times assume boiling water, which is more repeatable because the timing starts from a known point. Starting cold works but the time depends on how fast your hob brings the pan up, which varies by pan, quantity and stove.
Why are my eggs hard to peel?
Usually because they are very fresh. The membrane adheres more tightly to the shell in fresh eggs, and a week or two in the fridge makes peeling far easier. Plunging into iced water immediately after cooking also helps by contracting the egg away from the shell.
For steeping tea by type, see the tea brewing calculator. For converting cup measures to weights, see the cups to grams calculator.