Egg Boiling Time Calculator

Find the right boiling time for a soft, medium or hard egg based on its weight, how cold it starts, and how firm you want the yolk.

Quick Facts

Method
Williams (2005) heat-diffusion formula for a spherical egg
Time scales with egg mass2/3 and the temperature gap the yolk must close. Assumes the egg is fully submerged from the start of timing.

Your Results

Calculated
Boiling time
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Minutes : seconds in the water
Total time (minutes)
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Decimal minutes
Doneness
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Yolk result at this setting

Ready

Enter your egg details and press Calculate.

How long to boil an egg

The right boiling time is not a single number — it depends on how big the egg is, how cold it is when it goes in, and how firm you want the yolk. This calculator uses a physics-based formula rather than a fixed chart, so a small room-temperature egg and a jumbo fridge-cold egg each get their own answer.

As a quick reference, a standard large egg (about 57 grams) taken straight from the fridge and lowered into vigorously boiling water needs roughly:

  • Soft-boiled, runny yolk: about 4 to 4½ minutes (yolk centre near 63 °C)
  • Medium / jammy yolk: about 5 minutes (yolk near 65 °C)
  • Firm-set yolk: about 5½ minutes (yolk near 68 °C)
  • Hard-boiled, fully firm yolk: about 6 minutes (yolk near 70 °C)

The formula behind the numbers

The calculator implements the equation published by Dr. Charles Williams (University of Exeter) in Physics Education in 2005, which models the egg as a uniform sphere and asks how long heat takes to diffuse from the water to the centre of the yolk:

t = K · M2/3 · ln[ 0.76 × (Tegg − Twater) / (Tyolk − Twater) ]

Here M is the egg mass in grams, Tegg is the starting temperature, Twater is the water temperature, Tyolk is the target yolk temperature, and t comes out in seconds. The constant K (about 27.05) rolls together the egg's specific heat capacity (~3.7 J/g·K), density (~1.038 g/cm³) and thermal conductivity (~5.4×10⁻³ W/cm·K). Two things follow directly from the maths: cooking time grows with mass to the two-thirds power, so a 25 % heavier egg needs about 16 % longer, and it grows as the yolk's target moves closer to the water temperature.

Why starting temperature matters so much

A fridge-cold egg starts near 4 °C; a counter-temperature egg starts near 20 °C. Because the formula depends on the gap the yolk must close, a cold egg of the same size takes roughly a minute longer to reach the same doneness. Starting cold also reduces the chance the shell cracks from thermal shock, which is why many cooks lower eggs in gently with a spoon rather than dropping them.

Altitude and simmering water

Water boils below 100 °C at altitude — roughly 1 °F per 500 feet (about 1 °C per 275 metres) of elevation. If you cook at high elevation, or deliberately hold the water at a bare simmer, lower the water-temperature input to match; the calculator will lengthen the time automatically because the driving temperature gap is smaller.

Frequently Asked Questions

Should I start timing from cold water or boiling water?
This calculator assumes the water is already boiling (or at whatever temperature you enter) when the egg goes in and timing begins. That gives the most repeatable results because the egg experiences a known temperature from second zero. Cold-start methods, where eggs and water heat together, are also popular but their timing depends on your pot, burner and water volume, so they are harder to model precisely.
How do I stop the egg cooking at exactly the right point?
Residual heat keeps cooking the egg after you remove it, so transfer it straight into a bowl of ice water for 5 minutes or more. The cold bath halts carry-over cooking, keeps a soft yolk soft, and makes the shell far easier to peel by contracting the egg away from the membrane.
Why did my egg come out different from the calculated time?
The main variables are egg weight (weigh it if you can — "large" eggs range from about 50 to 63 g), how vigorously the water was boiling, and how many eggs you added at once. Adding several cold eggs briefly drops the water temperature, so cook in batches or add extra time. The model also assumes a fresh, un-cracked egg fully submerged the whole time.

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