Egg Doneness Calculator — boil, poach, coddle, sous vide with size + altitude correction

Egg doneness = yolk temperature, not cook time

Quick answer: doneness is defined by the peak temperature reached by the yolk center. At 62°C the yolk becomes custardy (thickens but flows). At 65°C it\u0027s jammy (spreadable). At 70°C firm. At 75°C+ fully set + chalky. Cook time is the mechanism to get the yolk to that temperature — affected by egg size, water temperature, start temperature, altitude, and cooking method. Changing any of those changes the cook time required to hit a given yolk temperature.

The 63°C egg (classic sous-vide preparation) is temperature-driven: the bath is 63°C, so the yolk CAN\u0027T exceed 63°C no matter how long you cook. That\u0027s why sous-vide gives consistent doneness — overshooting is physically prevented. Boiled eggs, by contrast, have yolk temperature rising through 100°C water; timing controls when you pull before the yolk sets too far.

Size scaling — the radius² law

Quick answer: heat penetration scales with the SQUARE of radius. A jumbo egg (63g) has ~17% larger radius than a large egg (50g); that\u0027s (1.17)² ≈ 1.37 scaling — ~37% more time to reach center temperature equivalent to large. This tool\u0027s size scaling factors (small 0.82× · medium 0.92× · large 1.00× · X-large 1.10× · jumbo 1.22×) approximate this radius² relationship per cube-root-of-mass geometric assumption.

In practice: if your recipe specifies large eggs + 7 min boil for soft-set, and you have jumbo eggs, use ~8.5 min. Conversely, small eggs + same soft-set doneness = ~5.7 min. Don\u0027t follow a large-egg recipe with jumbo eggs + expect runny yolks — you\u0027ll overshoot.

Altitude correction — water doesn\u0027t boil at 100°C at elevation

Quick answer: water boils when vapor pressure equals atmospheric pressure. At sea level, 100°C. As elevation increases, atmospheric pressure decreases, so water boils at lower temperature — approximately 1°C drop per 300m elevation. At 2000m (Denver, Colorado Springs), water boils at ~93°C. At 3500m (La Paz, Bolivia), ~89°C. At 4500m (Lhasa, Tibet), ~85°C.

Consequence: boiling eggs at elevation takes LONGER. The water is cooler, so heat transfer to the egg is slower, AND the peak temperature the yolk can reach is lower (yolk will reach ~93°C in Denver, not ~100°C). This changes "hard boiled" dynamics — eggs at elevation may never get truly hard without sous-vide-style direct temperature control. The tool extends time ~10% per 1000m for boil/steam methods. Sous-vide + coddled methods are altitude-independent (they don\u0027t rely on water boiling).

Sous vide vs boil — the precision-vs-tradition tradeoff

Quick answer: boiling is fastest + familiar but overshooting is easy (yolk rapidly moves from jammy to hard in the last 30 seconds). Sous-vide (immersion circulator at precise temperature) is slower (typically 30-60 minutes) but overshooting is impossible — the bath temp IS the final egg temp. For restaurant kitchens cooking eggs at scale, sous-vide is standard. For home breakfast, boil is faster + doesn\u0027t require the equipment.

Classic sous-vide egg temps: 60°C (yolk runny, white barely set, scrambled-esque when cracked) · 62°C (yolk thickens, white set but tender) · 63°C (the "63° egg" — fully liquid-gold yolk with slightly-firmer white) · 65°C (jammy) · 72°C (fully hard-boiled texture without the greenish ring). Time: 45 min is the full-penetration minimum for large eggs; past 60 min, texture is stable.

Why hard-boiled eggs sometimes have green-gray yolk rings

Quick answer: the green ring is iron sulfide (FeS) formed by reaction between iron in the yolk and hydrogen sulfide released from overheated albumen (egg white). Temperature + time are both factors: longer + hotter cook releases more H₂S; iron in yolk is always available. Sweet spot to avoid: <12 min boil for large egg; immediate ice bath post-cook halts the reaction. Fresh eggs have lower pH, which also reduces H₂S release — another reason very-fresh eggs don\u0027t green-ring as easily as older eggs.

The ring is aesthetic only — not harmful, not meaningfully changed in nutrition. But it signals overcooking, which also means rubbery white and chalky yolk texture. If your hard-boiled eggs routinely have green rings, reduce cook time 1-2 min and add ice bath.

Peelability — why fresh eggs are a pain to peel

Quick answer: fresh eggs (<3 days old) adhere tightly to their shells because the albumen pH is low (~7.5) — the protein pressed against the inner membrane. As eggs age, albumen pH rises (CO₂ leaves through the shell) to ~9+, which loosens the protein from the membrane. Older eggs (7-14 days past pack date) peel far more easily than very-fresh eggs.

Other peeling factors: (1) ice bath after cooking contracts the egg inside the shell slightly, creating a small gap; (2) older eggs have a larger air pocket at the blunt end, making peeling-start-point easier; (3) cracking + peeling under running water floats shell pieces away; (4) rolling the egg on a counter first creates micro-fractures that help peel. Combine all four for frustration-free peel.

What this model does not capture

Egg variation beyond size: shell thickness varies by breed + age + calcium intake; yolk-to-white ratio varies (20-35% yolk by mass); freshness affects white viscosity (fresh whites stay tight; older spread). The tool\u0027s timing is for typical USDA-grade eggs; farm-fresh or specialty (duck, quail, goose) will need separate calibration.

Carryover cooking post-heat is modest for in-shell eggs (shell slows heat exchange) but meaningful for out-of-shell poaching. If you pull a poached egg 30 seconds before your target, carryover finishes it; hitting target exactly overcooks.

Texture vs temperature isn\u0027t linear. Yolks rapidly transition from liquid to solid at 62-68°C; a 1°C difference in target creates a noticeable difference in perceived doneness. For sous-vide precision, use a thermometer-verified bath; for boiled, accept ±30 seconds variance as the practical minimum resolution of non-sous-vide cooking.

Sources and further reading

Harold McGee, On Food and Cooking 2nd ed. (Scribner, 2004) — Ch.2 covers egg chemistry + cooking comprehensively. J. Kenji López-Alt, The Food Lab: Better Home Cooking Through Science (W. W. Norton, 2015) — Ch.4 is the canonical modern egg-cooking reference with tested timings. Nathan Myhrvold et al., Modernist Cuisine Vol.4 Ch.11 (The Cooking Lab, 2011) — precision low-temperature egg cookery. Douglas Baldwin, Sous Vide for the Home Cook (Paradox Press, 2010 rev. 2012) — canonical home-sous-vide reference with egg-specific timing tables at various bath temperatures. For egg chemistry + denaturation: Belitz, Grosch, Schieberle, Food Chemistry 4e (Springer, 2009) Ch.11 on animal proteins. For altitude cooking: USDA Extension resources on high-altitude cooking + the historical High-Altitude Cooking by Shirley Corriher (various editions).