When the drinks are flowing at your Christmas Party, you probably pay no attention to the size of your wine glass.

Key points: Larger wine glasses could encourage us to drink more

Larger wine glasses could encourage us to drink more Wine glasses have doubled in size since 1990

Wine glasses have doubled in size since 1990 Experts say the size of our wine glass matters

But a new study has found that they are seven times larger than they were 300 years ago — and double the size of those in 1990.

Researchers think it is because wine is now cheaper and more readily available.

At Christmas parties plenty of us think it, maybe we even say it: the famous, "I'll only have a glass".

It's a sentence that's surely been uttered for hundreds of years, but in the past drinking even five glasses could have left you feeling remarkably sober.

Researchers at the University of Cambridge studied old glasses from museums and designs from manufacturers.

They found that in 1700, the average wine glass held just 66 millilitres of alcohol, the same as a double shot of spirits.

Today the average glass holds 449 millilitres.

But wine expert Gilbert Winfield said it is not what it seems.

"That isn't necessarily because we've turned into hopeless alcoholics, at least I hope it's not. We're drinking differently from what we were several hundred years ago, certainly we were drinking a lot more fortified wines in those days, which are stronger in alcohol and which would then have been served in smaller glasses," he said.

Graph shows wine glasses now hold 450ml, as opposed to 70ml in 1700 ( BMJ )

Scientists do suspect larger glasses do encourage us to drink more by tricking our brains into thinking there's more to get through.

But wine-tasting specialists like Mr Winfield point out that we now tend to make glasses bigger to enhance our enjoyment of the wine.

His advice is not to drink too quickly and to remember that a glass half full is plenty.

University of Cambridge Professor Theresa Marteau conducted an experiment at the Pint Shop in Cambridge in 2016, altering the size of wine glasses while keeping the serving sizes the same.

It resulted in a 10 per cent increase in sales.

"Wine will no doubt be a feature of some merry Christmas nights, but when it comes to how much we drink, wine glass size probably does matter," she said.

AP