The number that makes international comparisons misleading
In the UK, one "unit" of alcohol contains 8 grams of pure ethanol. In France, Spain, Portugal, and most of continental Europe, one standard drink contains 10 grams. In the US, a standard drink contains 14 grams -- nearly twice the UK unit.
This matters because weekly drinking guidelines are expressed in these local units. The NHS recommends no more than 14 units per week -- that is 112 grams of alcohol. France recommends 10 standard drinks per week -- 100 grams. The US CDC recommends up to 14 drinks per week for men -- 196 grams. The US limit, in other words, is almost double the French or UK limit when converted to actual alcohol content.
Work out your real weekly alcohol intake with the alcohol units calculator.
Why UK guidelines changed -- and what "unit" actually means in a glass
A 175 ml glass of wine at 13 % ABV contains 2.3 UK units. A pint of 4 % lager is 2.3 units. Many people significantly underestimate their consumption because they count drinks rather than units.
The NHS 14-unit weekly guideline applies equally to men and women, a change introduced in 2016 when evidence showed women face similar long-term health risks at lower consumption levels than was previously thought. The old guidance for men (21 units) was based on research that has since been updated.
The comparison problem: different definitions, same number
When a French study says "10 verres par semaine" and a UK study says "14 units per week", they are almost identical in grams of alcohol (100 g vs 112 g). When a US study says "14 drinks per week", it refers to 196 g -- nearly double. Reading health research without noting the local definition of a standard drink makes comparisons unreliable.
If you have read guidelines from US health sources, you may be applying limits that are significantly higher than what UK or European authorities recommend for equivalent health risk.