What do egg sizes mean in a recipe?

The UK weight bands, which recipes actually care, and how to substitute one size for another by weight.

Difficulty: beginner
Time: 5 min
Read: 3 min

Short answer

UK recipes assume a medium egg unless they say otherwise — about 53 to 63g in shell, or roughly 50g of egg. For baking, weigh the eggs instead of counting them: 50g per medium egg is the conversion that works.

Egg size is one of the quiet variables in baking. Three large eggs instead of three medium is an extra 30 to 40g of liquid, which in a small sponge is enough to change the texture noticeably.

Step by step

Learn the UK bands.Small under 53g, medium 53 to 63g, large 63 to 73g, very large 73g and over. Those are weights in the shell.
Assume medium unless told otherwise.UK recipes are written for medium eggs by convention. American recipes assume large, which are close to UK medium-to-large — one reason US bakes sometimes come out wet here.
Weigh rather than count for baking.About 50g of egg out of the shell per medium egg. If a recipe wants three eggs, 150g of beaten egg is what it means.
Remember the ratio inside the egg.Roughly two-thirds white to one-third yolk by weight. A medium egg is around 33g white and 17g yolk, which matters when a recipe wants one or the other.
Care about size in delicate bakes.Sponges, macarons, custards, meringues and choux are sensitive. A one-egg difference in liquid changes the batter.
Stop worrying for robust cooking.Scrambled eggs, omelettes, frittatas, fried eggs, most quick breads and anything with a wide margin do not care what size the egg is.
Adjust when substituting.Three large eggs instead of three medium is about 30g extra. Beat all three, weigh out 150g and hold the rest back.
Use spare white and yolk rather than binning them.Both keep several days covered in the fridge and both freeze.

Tips

50g per medium egg is the number to remember.
US recipes assume large eggs; UK recipes assume medium.
For anything fussy, beat the eggs and weigh out what you need.

Common mistakes

Using large eggs in a small sponge recipe written for medium — Three large eggs adds roughly 30 to 40g of extra liquid to a mixture that might only be 500g in total, which loosens the batter and gives a wetter, denser crumb.
Assuming egg size never matters — It does not matter for a frittata and it very much does for a genoise or a custard, where the ratio of egg to everything else is the recipe.

If it doesn't work

Sponge wetter and denser than expected

Cause: Eggs too large — Fix: Weigh the eggs — 50g per medium — and hold back the excess.

Mixture too stiff

Cause: Eggs too small — Fix: Add beaten egg a little at a time until it reaches the described consistency.

Custard did not set

Cause: Not enough yolk — Fix: Weigh the yolks: about 17g each. Small eggs can leave a custard short.

Meringue slack

Cause: Whites heavier than assumed — Fix: Weigh the whites and use 50 to 60g of sugar per 30g of white.

Questions people ask

How much does an egg weigh without the shell?

About 50g for a medium egg, made up of roughly 33g white and 17g yolk. A large egg is about 58g out of the shell.

Does egg size matter for scrambled eggs?

No. Anything cooked to a texture rather than a ratio is unaffected. Size matters in baking, custards and meringues, where the proportions are the recipe.