Only have medium eggs but the recipe wants large? Convert by liquid weight and get the right whole-egg count, with the remainder noted.
Recipes are almost always developed with large eggs. When you swap in a different size, what actually matters is the total liquid egg going into the batter — so the right way to substitute is by weight, then round to whole eggs.
For example, 3 large eggs are 150 g of liquid egg. Divided by 44 g for a medium egg, that's 3.4 — so you'd use 3 medium eggs and you'd be a little short, which is fine for most bakes.
USDA sizes are set by minimum weight per dozen. These are the typical liquid weights without the shell:
| Size | Liquid (no shell) |
|---|---|
| Peewee | 29 g |
| Small | 37 g |
| Medium | 44 g |
| Large | 50 g |
| Extra-large | 56 g |
| Jumbo | 63 g |
Swapping one size up or down is rarely a problem — a single egg's variance is small and most batters are forgiving. It matters most when a recipe uses several eggs, where the difference compounds.