The difference is about 10% which is easily noticeable. Typically in a British pub you will be served beer in a glass that is calibrated as “pint to brim”, and

The difference is about 10% which is easily noticeable. Typically in a British pub you will be served beer in a glass that is calibrated as “pint to brim”, and any head on the beer is taken out of the nominal pint. So usually a pint as served is much closer to half a litre.