A glass of red wine is 250ml.
A standard size bottle of wine (750ml) serves five or six glasses, but the hospitality industry usually goes for five out of a bottle. 150ml (or 5oz) is what you can reasonably expect in restaurants and bars for the average glass of wine.
Do you honestly pour a third of a bottle at a time for wine?
175ml and 125ml are also UK standards but in a lot of places if you order wine by the glass you'll get 250ml.
For the UK this is all not that relevant, because there the concept of the 'alcohol unit' is much more ingrained and used in public health campaigns, so you would work with those. E.g., with the recommended upper limit of 14 alcohol units, you could drink a standard glass of wine (175ml) six days of the week (12.6 units), or have a bottle of lager six days of the week and a pint of Guinness on Saturday (13.2 units).
1: https://www.nhs.uk/live-well/alcohol-support/calculating-alc...