A standard drink size varies depending on what sort of alcohol you are drinking.
A standard drink is considered to be 10g of alcohol. So therefore the volume of a standard drink will vary depending on the % of alcohol that is the drink.
For example : If you are drinking wine and it says it is 10% alcohol. That means it has 10g of alcohol for 100ml of wine. (ie 10g / 100ml x 100 = 10%). So standard drink of that wine is only 100ml.
Now it gets a bit more tricky when the % is not 10%. Just say a beer is 5.5% alcohol. That means it has 5.5g of alcohol per 100ml of beer. 200ml of beer would give you 11g of alcohol. Just over 1 standard drink.
This is why many companies now have to write how many standard drinks there is in each bottle of alcohol on the side. As it is very complicated to work out when sober!!!
Now if you are going to drink wine or spirits in a bar it can be difficult to work how much alcohol you have had as wine can vary in it’s percentage of alcohol. Spirits can also vary. It helps though to know that a nip/shot is 30ml. So if a spirit is 30% alcohol (30g per 100ml) and you have 1 shot of 30ml then you are having about 10g of alcohol in each shot. Some spirits can be higher then this and some lower.
So if you have a favourite drink it helps to look at a bottle of it and see what the percentage alcohol is.
eg Kahlua is 20% alcohol
Therefore 100ml has 20g of alcohol. If you had 3 shots of 30ml = 90 ml total you will have had nearly 20g or 2 standard drinks.
How to Calculate for any alcohol.
1. What is the % alcohol (15%)
2. That means how many grams per 100ml (15 g of alcohol)
3. How many mls am I drinking (200ml)
4. How many standard drinks is that (200ml = 30g of alcohol= 3 standard drinks)