Find the right boiling time for eggs from boiling water, based on egg size and desired doneness.
This calculator is based on the method where the egg is placed directly into already boiling water, then simmered for the stated time. Take the egg straight from the fridge — if the egg is at room temperature instead, the boiling time may be a bit shorter. After boiling, it's a good idea to cool the egg quickly in cold water to stop further cooking and make it easier to peel.
The time is adjusted slightly for egg size — smaller eggs need about a minute less, extra large eggs need about a minute more.
The calculator assumes the egg is straight from the fridge. If the egg is at room temperature, the boiling time can be a bit shorter since it takes less time for the heat to reach the center.
Rapid cooling stops residual heat from continuing to cook the egg inside the shell, and makes the shell easier to remove since it shrinks slightly faster than the egg itself.
The green ring occurs when the egg is boiled too long or isn't cooled quickly enough afterward — iron from the yolk reacts with sulfur from the white to form iron sulfide. It's safe to eat, but is most easily avoided with correct boiling time and rapid cooling.