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Egg Boiling Calculator

Achieving the ideal boiled egg requires precision: heat transfer depends on egg size, starting temperature, and atmospheric pressure. This calculator accounts for all three variables—including altitude effects on water's boiling point—to predict exact cooking times for soft-set whites with runny yolks, half-set yolks, and fully hard-boiled eggs. Cooks at high elevations especially benefit from accounting for the reduced air pressure that extends cooking duration.

Last updated:

Creators Łucja Zaborowska, MD, PhD
8,639 people find this calculator helpful

How Eggs Cook in Hot Water

When an egg enters boiling water, heat conducts inward from the shell through the white (albumen) and toward the yolk. The key to perfect texture lies in understanding that these components coagulate at different temperatures. Egg white sets around 63–65 °C (145–150 °F), whilst the yolk remains liquid until roughly 70 °C (158 °F).

A soft-boiled egg exploits this gap: you halt heating once the white has firmed but the yolk stays runny. For a half-boiled egg, both components have begun to set, though the yolk's centre remains soft. Hard-boiling requires sustained heat until the yolk is fully opaque and firm throughout. Egg size and initial temperature both shift these timings—a cold egg from the fridge requires longer than one at room temperature.

Boiling Time Prediction

Cooking time depends on egg mass, initial temperature, and the ambient boiling point of water. The equations below estimate the time required to reach each doneness level:

soft_egg_time = f(weight, temperature, boiling_point)

half_boiled_egg_time = g(weight, temperature, boiling_point)

hard_egg_time = h(weight, temperature, boiling_point)

boiling_point = (49.161 × ln(pressure) + 44.932 − 32) × 5/9

pressure = 29.921 × (1 − 0.0000068753 × altitude)^5.2559

  • weight — Egg mass in grams
  • temperature — Starting temperature of the egg (fridge or room temperature)
  • boiling_point — Boiling point of water at your altitude, in degrees Celsius
  • pressure — Atmospheric pressure at your location
  • altitude — Height above sea level in metres, affects air pressure and thus boiling point

Why Altitude Matters More Than You'd Think

At sea level, water boils at 100 °C (212 °F). But as altitude increases, atmospheric pressure drops, and so does water's boiling point. Every 300 metres of elevation reduces the boiling point by roughly 1 °C.

In the city of El Alto, Bolivia (3,640 m / 11,942 ft elevation), water boils at approximately 87 °C (189 °F). At the summit of Mount Everest (8,848 m / 29,029 ft), it drops to just 68 °C (154 °F)—making it nearly impossible to hard-boil an egg with traditional timing. Even modest elevations of 1,500–2,000 metres can add several minutes to cooking time. If you live in a mountainous region or are travelling to higher altitudes, entering your location's elevation ensures the calculator returns realistic durations.

Common Mistakes and Practical Tips

Precise timing is only half the battle; several other factors determine success.

  1. Cold eggs crack in boiling water — Eggs taken straight from the refrigerator risk cracking when plunged into hot water due to thermal shock. Let them sit at room temperature for 5–10 minutes beforehand, or gently lower them into water using a spoon. Adding half a teaspoon of salt also strengthens the shell.
  2. Water volume affects heating rate — Insufficient water cools dramatically when cold eggs enter it, extending actual cook time unpredictably. Use at least three times the egg volume in water and bring it to a rolling boil before adding eggs. This keeps temperature stable.
  3. The ice bath stops overcooking — Once your timer sounds, transfer eggs immediately to ice-cold water. Even out of the pot, residual heat continues cooking the yolk for another minute or two. A rapid chill halts this carryover effect and sets texture precisely.
  4. Egg freshness and size vary cooking time — Fresher eggs are slightly denser and conduct heat differently than older ones. Size variation (even within a 'medium' category) can shift times by 30–60 seconds. Use the weight input option for maximum accuracy if your eggs vary significantly from standard sizes.

Quick Reference Times at Sea Level

For a medium egg (50–55 g) starting at room temperature (20 °C / 68 °F) at sea level:

  • Quarter-boiled: approximately 3 minutes (soft white, almost entirely liquid yolk)
  • Soft-boiled: approximately 5–6 minutes (firm white, runny yolk)
  • Half-boiled: approximately 6–7 minutes (set white, soft but thickened yolk)
  • Hard-boiled: approximately 9–10 minutes (fully set white and yolk)

Fridge-cold eggs require an extra 1–2 minutes for each stage. Larger eggs (60+ g) add 30–60 seconds; smaller eggs (under 50 g) subtract similar amounts.

Frequently Asked Questions

How much longer do eggs take to boil at high altitude?

The effect scales with elevation. At 1,500 metres (4,920 ft), expect 1–2 additional minutes compared to sea level. At 3,000 metres (9,843 ft), add 3–4 minutes. The relationship is non-linear: air pressure drops exponentially with altitude, so each thousand metres has a compounding effect. High-altitude cooking often requires trial and error unless you account for both altitude and initial egg temperature.

Can the number of eggs in the pot change cooking time?

No. The time depends only on heat transfer into individual eggs, determined by their size, starting temperature, and the boiling point of water around them. Batch size affects only the volume of water needed and how quickly the water returns to a boil after adding eggs. Use a large pot with plenty of water so the temperature remains stable, but don't worry—ten eggs take the same duration as one egg.

What is a quarter-boiled egg, and who eats them?

A quarter-boiled egg has a barely set white and a yolk that is almost entirely liquid. This doneness is most common in British and European cuisines, where eggs are served in eggcups with soldiers (thin strips of toast). It requires very precise timing—only 3–4 minutes for a room-temperature medium egg at sea level. The yolk runs into the white and onto the toast, making a rich, custardy bite.

Should eggs be added to cold or boiling water?

Bring water to a rolling boil first, then gently place eggs in using a spoon. Boiling water cooks the white faster and more evenly, reducing the risk of a grey-green ring forming around the yolk due to iron-sulphur compounds. Starting in cold water produces uneven cooking. Once eggs are in, the water temperature will drop slightly; return it to a boil as quickly as possible.

How do I know when my eggs are done without a timer?

Timing is your most reliable method, but visual and tactile cues help. Soft-boiled eggs wobble when tapped gently; hard-boiled eggs feel solid throughout. A cracked egg shell reveals the white's colour and firmness. However, these checks are imprecise compared to the calculator. For consistent results, especially when cooking for guests, always use a timer adjusted for your altitude and egg temperature.

Why do some eggs have a grey-green ring around the yolk?

This ring forms when iron in the yolk reacts with sulphur in the white under prolonged heat, creating ferrous sulphide. It's harmless but indicates overcooking. Use the calculator to hit your target time exactly, cool eggs immediately in ice water, and avoid re-heating. Starting with boiling water (rather than cold water) and using fresh eggs also reduces the risk.

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