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How to Use the Calculator
1. Size: Start by selecting your egg's size, as printed on the carton.
2. Temperature: Are you cooking straight from the fridge or with a room-temperature egg? This makes a big difference!
3. Altitude: If you're not sure, a quick search for your city's altitude will work. Most people can leave this at 0 meters.
4. Doneness: Slide to your perfect yolk. Our visual guide below will help you choose!
A Visual Guide to Egg Doneness
Runny Yolk (62°C)
Liquid yolk, perfect for dipping.
Jammy Yolk (70°C)
Custardy and soft, ideal for salads.
Firm Yolk (77°C)
Cooked through, but still tender.
Hard Boiled (83°C)
Firm and crumbly, for deviled eggs.
The Science Behind the Perfect Egg
This calculator isn't based on guesswork; it's based on physics. It uses a formula derived from Fourier's equation for heat conduction to model how heat travels from boiling water to the center of the egg's yolk.
Why Size Matters: The formula accounts for the egg's mass. Just like a large potato takes longer to bake than a small one, a larger egg requires more time for heat to penetrate to its center.
The Cold Start Problem: A significant amount of energy (and time) is needed to raise an egg's temperature from fridge temperature (4°C) to its target. A room temperature egg (20°C) has a head start, so it cooks faster.
High Altitude Cooking: Water boils at a lower temperature at high altitudes. At 1,600 meters (about a mile high), water boils around 95°C instead of 100°C. This lower temperature water has less heat energy, so cooking takes longer.
What's in a Degree?: "Doneness" is simply the final temperature of the yolk. A liquid yolk is achieved around 62°C, a custardy "jammy" set happens around 70°C, and a fully firm, crumbly yolk requires about 83°C.
Pro Tips for Perfect Eggs
- The Water: Always use enough water to cover the eggs by at least an inch. For the most accurate timing, start with already-boiling water, as the calculator assumes this.
- Preventing Cracks: To reduce thermal shock, let refrigerated eggs sit on the counter for 10 minutes before boiling. Use a spoon to gently lower them into the water.
- The Ice Bath: This is the secret to stopping the cooking process instantly and making eggs easier to peel. As soon as the timer goes off, transfer eggs to a bowl of ice water for at least 5 minutes.
Did You Know?
No More Green Rings
The green ring you sometimes see around a hard-boiled yolk is harmless iron sulfide. It forms when you overcook the egg. An ice bath helps prevent it!
Older is Better (for Peeling)
An older egg is often easier to peel than a very fresh one because its pH increases over time, causing the white to adhere less to the shell membrane.
Frequently Asked Questions
Should I put my eggs in cold water or boiling water to start?
For the most precise timing, this calculator assumes you are gently lowering your eggs into water that is already at a rolling boil. Starting in cold water also works, but the timing is less predictable as it depends on your stove's power.
Why did my eggs crack when I boiled them?
Eggs usually crack from "thermal shock"—when a cold egg is dropped into very hot water. You can reduce this risk by letting eggs sit out of the fridge for 10-15 minutes or by lowering them into the water very gently with a spoon.
What is the green ring around my hard-boiled yolk? Is it safe to eat?
The green or grayish ring is iron sulfide, and it's completely harmless. It forms when hydrogen sulfide in the egg white reacts with iron in the yolk, usually as a result of overcooking.
How can I make my eggs easier to peel?
The most effective method is to immediately transfer the cooked eggs into an ice bath for at least 5 minutes. This shock helps the egg membrane separate from the shell. Also, slightly older eggs tend to be easier to peel than farm-fresh ones.
How long can I store hard-boiled eggs?
You can store hard-boiled eggs (peeled or unpeeled) in the refrigerator for up to one week. It's best to store them in an airtight container.