How to use it
- Choose your Sex and enter your Body weight in kilograms.
- Enter the Number of drinks, the Volume of each drink in millilitres and its Strength as a percentage.
- Enter the Hours since the first drink, then read the Peak blood alcohol and the times to 0.0, 0.2 and 0.5.
How the estimate is calculated
The Widmark formula estimates blood alcohol from the grams of alcohol drunk, the body weight and a distribution factor for body water. The factor is 0.68 for men and 0.55 for women in Widmark's original formula. The grams of alcohol are the volume of each drink, times its strength, times the density of ethanol, 0.789 grams per millilitre.
Alcohol leaves the blood at about 0.15 per mille an hour on average, according to Jones (2010), as quoted on Wikipedia. Individual rates range from about 0.15 to 0.20 an hour, so the times on this page are estimates and can be too long or too short for you.
This is not medical advice, and no estimate can say that a person is safe to drive. Never drive after drinking. Food, speed of drinking, body build, illness and some medicines change the real level, and a drink that feels small can still matter.
Grams of alcohol A = drinks x ml x (strength / 100) x 0.789
Peak per mille = A / (r x body weight in kg), r = 0.68 men, 0.55 women
Level after t h = peak - 0.15 x t, never below 0What the estimate leaves out
- Legal limits. This page does not show the blood alcohol limits for driving in any country.
- Food in the stomach, which slows absorption, and the speed of drinking.
- Medicines, illness, pregnancy and any condition that changes how the body handles alcohol.
Worked example: man, 70 kg, two 500 ml drinks at 5 %
The drinks hold 2 x 500 x 0.05 x 0.789 = 39.5 g of alcohol. The peak is 39.45 / (0.68 x 70) = 0.83 per mille.
Falling at 0.15 per mille an hour, the level reaches zero after 0.83 / 0.15 = 5.5 hours, which is 5 h 32 min. It reaches 0.2 after 4 h 12 min and 0.5 after 2 h 12 min.
| Level | Time from the first drink |
|---|---|
| Peak | 0.83 per mille |
| 0.5 per mille | 2 h 12 min later |
| 0.2 per mille | 4 h 12 min later |
| 0.0 per mille | 5 h 32 min later |
Frequently asked questions
Why is the time to zero longer than I expected?
The elimination rate is about 0.15 per mille an hour on average, and many people clear alcohol at a similar rate. Drinking more slowly lowers the peak, but the time to zero depends on how much you drank in total.
Why do men and women get different results?
The Widmark factor for body water is 0.68 for men and 0.55 for women, so the same drinks give a higher level in a woman of the same weight. Body build and fat also matter.
Can a calculator tell me I am safe to drive?
No. This estimate cannot show that anyone is safe to drive, and the rate of elimination varies from person to person. Never drive after drinking.
What is a standard drink?
Wikipedia, citing the US definition, gives a standard drink as 14 grams of alcohol, about 17.7 ml of pure alcohol. Other countries define it differently, so check the label's volume and strength.
What should I do if someone has drunk too much?
Do not leave them alone, keep them on their side, and get medical help straight away if they are confused, cannot wake up properly, or are vomiting.
Are my drinks and weight stored or sent anywhere?
No. The estimate is calculated in your browser and nothing you enter is sent to us.
Sources
- Blood alcohol content, Widmark formula, elimination rate (Wikipedia)
- Ethanol, density at 20 C (Wikipedia)
Figures and text last checked on Tuesday, November 10, 2026.