I thought it was 300mL since I'm a little familiar with teapot sizes and a 300mL pot holds about one small glass of water... and 8oz is a "serving" of a liquid drink.
This is not the best answer. 8oz is 237mL so the best answer is 250mL.
@futurebird We have two 2-cup Pyrex measuring cups with cup fractions marked on one side and milliliters on the other, so the conversion is reinforced frequently.
@futurebird
Isn't it 227? The number I have stored in my head is 454, which is g to the pound. Since a pint's a pound and a mL of water weighs a gram, I assumed 8 fl. oz. (half a pint) would weigh half of 454 g and contain 227 mL.