• In a new experiment, when drivers were asked to free pour a 175ml glass of wine, 62 per cent overpoured, while 51 per cent overpoured a 125ml glass
  • When asked to pour a single measure of spirits – one in six poured a double measure
  • Nearly five million drivers (14 per cent) in the last six months may have been over the drink drive limit

A new study1 by Direct Line Car Insurance exposes the risk of driving over the legal alcohol limit due to a lack of understanding of alcohol measures, which sees people pour excessively large glasses containing several units of alcohol. In a practical experiment testing drivers’ ability to pour set limits of alcohol, 56 per cent of participants over poured when asked to fill a glass with standard pub measures of wine.

The experiment tested 100 drivers’ ability to free pour pub standard measures of alcohol, investigating whether when drinking at home or at barbecues and picnics, drivers could be over the legal alcohol limit without realising.  Over half (51 per cent) of participants poured more than 125ml when asked to fill a glass with this measure, 13 per cent poured at least a 175ml sized glass and one in 20 poured over 200ml. When asked to pour out a 175ml glass, nearly two thirds (62 per cent) over poured and 14 per cent poured the equivalent of at least a 250ml glass of wine containing a minimum of 3.2 units2 of alcohol.

Spirits are even tougher to estimate, with three quarters (75 per cent) of participants over pouring a single 25ml spirit measure and one in six (18 per cent) pouring at least a double (50ml) instead of a single.  When asked to pour a double, nearly two thirds (63 per cent) poured more than the correct 50ml of spirits. Almost a quarter (24 per cent) poured at least a treble (75ml) and one in 12 (eight per cent) went so far they poured 100ml, a quadruple measure. Pouring spirits over ice led to a greater proportion of participants overpouring both a single (77 per cent) and a double (64 per cent) measure.


Table one: Drivers who over poured standard measures of alcohol

Size of measure Wine Spirit Spirit with ice
Small (125ml) 51%
Medium (175ml) 62%
Single (25ml) 75% 77%
Double (50ml) 63% 64%

Source: Direct Line Car Insurance 2020

The average size of a home measure is much greater than a standard pub or restaurant measure.  However, the average volume of a glass of wine a person pours for themselves at home is 190ml, with men pouring slightly more (200ml) than women (180ml). Nearly a fifth (18 per cent) of drivers when having a glass of wine pour at least 250ml, equivalent to a third of a bottle of wine. The average home spirit measure is 62ml, which is more alcohol than if ordering a double in a bar or restaurant, while for a quarter of people (25 per cent) their homemade G&T would include at least a treble measure of gin (75ml).

It is not just when pouring for themselves there is an issue, people are unable to judge volumes of alcohol when a glass is poured for them3.  When looking at glasses of wine, only 30 per cent of people could correctly identify a 125ml glass, while almost a third picked a glass with more alcohol in. When asked to identify a 175ml glass of wine, only one in eight (12 per cent) managed to select correctly, with 39 per cent choosing a glass with a greater volume.

Spirits are equally difficult to identify, as under a third (29 per cent) of people were able to correctly identify a single 25ml shot.  Identifying a double is even more challenging, just one in eight (16 per cent) could correctly identify the correct 50ml measure.  If people are poured a glass of wine or G&T by a friend or family member and then go on to drive, they could find themselves in excess of the drink drive limit after just one glass.

Drink driving risks

Of motorists who drink alcohol and drive, nearly one in five (18 per cent) would drink alcohol if they were the designated driver. One in nine (11 per cent) insist on pouring their own measures but three million motorists (seven per cent) would allow others to do it for them.  As the experiment revealed these drivers could find themselves over the drink drive limit without realising.

Over the last six months alone, nearly five million (14 per cent) motorists have driven their car when they thought they were over the limit, with over two million (six per cent) believing this to be because the person serving them poured larger drinks than they realised.

There is widespread confusion about the legal limit for consuming alcohol and driving across the UK. Just four per cent of drivers in Scotland and just 12 per cent of drivers living in England, Wales or Northern Ireland know what the legal limit is for where they live.  The drink driving limit in England, Wales and Northern Ireland is 35 micrograms of alcohol per 100 millilitres of breath, while in Scotland it is just 22 micrograms of alcohol per 100 millilitres3.

Steve Barrett, head of motor insurance at Direct Line commented: “It isn’t just the safety of the driver and passengers in their car that are at risk if a driver is over the limit, it is everyone else on the road too. This experiment shows that home measures are often substantially more generous than those measured in a pub or restaurant and how just one glass of wine or a spirit poured at home could put a driver over the drink drive limit.

“Due to the impact of Covid-19 more people will be drinking at home rather than drinking out in pubs and restaurants. If a driver chooses to have a drink at home or at someone else’s house within their ‘bubble’, it is vital they know how much alcohol they are consuming, before getting behind the wheel. The only way anyone can be sure that they are safe to drive in this situation, is if they don’t have any alcohol at all.”

  1. 100 participants with ages ranging from 18-86 participated in the experiment, which took place in July 2020. The gender split was 56% women and 44% men. Participants were asked to free pour their standard home measures of both wine and spirits and then pour what they believed to be 125ml and 175ml glasses of wine and 25ml and 50ml measures of spirits, both with and without ice.
  2. https://www.drinkaware.co.uk/facts/alcoholic-drinks-and-units/units-and-calories-in-alcoholic-drinks/red-wine
  3. Research conducted by Opinium among a nationally representative sample of 2,000 UK adults between 31st July -4th August 2020
  4. UK drink drive limits – https://www.gov.uk/drink-drive-limit