Egg Cooking Time Calculator
Find the ideal boiling time for a perfect soft, medium, or hard-boiled egg based on egg size and your preferred doneness. Removes the guesswork from one of cooking's most precise tasks.
About this calculator
Egg cooking time depends on the mass of the egg and how set you want the yolk and white. This calculator uses a base cooking time adjusted by an egg size factor. The formula is: cookingTime = baseTime + (baseTime × 0.125 × eggSize). Here, baseTime represents the starting duration for a small egg at your chosen doneness, and eggSize is a numeric modifier (e.g., 1 for medium, 2 for large, 3 for extra-large). Each size increment adds 12.5% of the base time, accounting for the greater thermal mass that larger eggs present. The underlying physics is heat conduction through the albumen to the yolk center; larger eggs simply require more time for the heat to penetrate fully.
How to use
Imagine you want a soft-boiled large egg where the base time is 6 minutes and the eggSize modifier is 2. Plug the values into the formula: cookingTime = 6 + (6 × 0.125 × 2) = 6 + 1.5 = 7.5 minutes. So you should boil your large egg for 7 minutes 30 seconds for a runny yolk and fully set white. For an extra-large egg (eggSize = 3) with the same base time: cookingTime = 6 + (6 × 0.125 × 3) = 6 + 2.25 = 8.25 minutes, or about 8 minutes 15 seconds.
Frequently asked questions
How does egg size affect boiling time for soft or hard-boiled eggs?
Larger eggs contain more mass, which means heat from the boiling water takes longer to penetrate to the center of the yolk. A medium egg might reach a soft-boiled state in around 6 minutes, while an extra-large egg needs closer to 8 minutes for the same result. Ignoring size differences is one of the most common reasons home cooks end up with unexpectedly runny or overcooked eggs. Using a size-adjusted formula accounts for this thermal difference precisely.
Should I start eggs in cold water or boiling water for accurate cooking times?
Starting eggs in already-boiling water gives far more consistent and predictable results, and most precise cooking-time formulas — including this one — assume you lower the egg into simmering or boiling water. Cold-start methods involve a variable heating phase that differs by pot, stove, and water volume, making timing unreliable. If you prefer the cold-start method, add approximately 1–2 minutes to the calculated time and expect some variation. For perfect precision, use boiling water and a timer.
Why do altitude and water temperature affect egg boiling times?
At higher altitudes, atmospheric pressure is lower, which causes water to boil at temperatures below 100 °C (212 °F). At 2,000 meters above sea level, water boils at roughly 93 °C, meaning less heat energy is transferred to the egg per minute. As a result, eggs take noticeably longer to cook at altitude — sometimes 20–30% more time than at sea level. If you live or cook above 1,500 meters, you should add extra time beyond the calculator's output or use a pressure cooker to restore full boiling temperature.