A jumbo egg doesn’t need proportionally more time than a medium one to reach the same doneness — heat has to penetrate through the whole egg, and that penetration time scales with mass^(2/3), not mass itself.
This comes directly from heat-diffusion physics: doubling an egg’s mass doesn’t double the distance heat has to travel to the centre, so cooking time grows slower than mass does — a genuinely counter-intuitive result most kitchen advice ignores entirely.
It assumes the egg starts at a known, uniform temperature. Straight from the fridge against room temperature is worth more than the size difference the rule is correcting for — and at altitude the water is not at 100 °C, which changes the driving temperature the whole model rests on.
Estimate with the rule, then check it against the calculator that models it properly.
Open Egg Timer Calculator →A jumbo egg doesn’t need proportionally more time than a medium one to reach the same doneness — heat has to penetrate through the whole egg, and that penetration time scales with mass^(2/3), not mass itself. This comes directly from heat-diffusion physics: doubling an egg’s mass doesn’t double the distance heat has to travel to the centre, so cooking time grows slower than mass does — a genuinely counter-intuitive result most kitchen advice ignores entirely.