On the size of eggs

I often don’t have the correct size of eggs in to follow a recipe.  If I only have large eggs, how many should I use when the recipe calls for small eggs?  With only medium yolks, how many should I use when a recipe calls for small yolks?

Small eggs weigh approximately 50g, medium eggs 60g, and large eggs 70g.  Large eggs are roughly 15% larger than medium eggs (70 / 60 = 1.17), and small eggs are roughly 15% smaller than medium eggs.

For example, if you only have large eggs, but a recipe calls for 6 medium egg yolks, do the following sum:
6 x 20g of yolk [from picture above, showing a medium egg] = 120g.  Large egg yolk weighs 15% more than a medium egg yolk, or 1.15 x 20g = 23g.  120g of yolk in large egg yolks = 120/23 = 5.2 yolks.  This rounds to 5.  So for 6 medium egg yolks, you will only need 5 large ones.

Yes, it’s tough without a calculator, but memorising the picture above definitely helps!