BAC Tool
Estimate blood alcohol concentration using body weight, distribution factor, drinks consumed, alcohol strength, drinking duration and elapsed time. Explore a projected BAC curve, estimated peak, clearance time, standard drinks and an itemised beverage breakdown.
| Drink | Servings | Alcohol (g) | Standard drinks |
|---|---|---|---|
| Total | — | — | — |
The Widmark-based calculation is a rough model, not a breathalyser or blood test. It assumes steady consumption and clearance, and does not reliably capture absorption delays, meals, medication, health factors or individual differences. BAC can continue rising after the last drink. No calculated value proves sobriety or fitness to drive.
Table of Contents
Highlights
- Personalised BAC estimate using weight and body-water factor
- Multiple beverages with quantity, serving size and ABV
- Interactive BAC-over-time graph with current-time marker
- Estimated peak BAC, clearance time and standard drinks
- Detailed drink breakdown with CSV, JSON and PNG exports
How BAC Tool Works?
The calculation uses a simplified Widmark model. Each beverage contributes pure alcohol according to serving volume, quantity and alcohol by volume (ABV). The calculator uses an alcohol density of 0.789 g/mL.
Here, A is total alcohol in grams, n is the number of servings and V is the volume of each serving in millilitres. The initial BAC estimate divides the alcohol dose by body mass and the selected body-water distribution factor.
W is body weight in kilograms and r is the distribution factor (presets 0.68 and 0.55, or a custom value from 0.40 to 0.80). The model distributes drinking evenly over the entered period, then subtracts alcohol clearance at a fixed BAC percentage-point rate per hour.
For a positive drinking period D, p(t) = min(1, max(0, t/D)); when D = 0, p(t) = 1 from the first drink. The selected clearance rate k is 0.010, 0.015 or 0.020 BAC percentage points per hour, or a custom value from 0.005 to 0.030. Estimated time remaining until zero is current estimated BAC divided by k. The estimated peak occurs at the end of drinking if the rising dose exceeds clearance, otherwise at the start.
| Result | How it is determined |
|---|---|
| Estimated BAC now | BAC(t) at the entered hours since the first drink, shown as a percentage |
| Estimated peak BAC and time | Highest modelled value and its time since the first drink |
| Time until estimated zero | Current BAC divided by the selected hourly clearance rate |
| Standard drinks | Total pure alcohol divided by the selected 10 g or 14 g definition |
| Graph and drink breakdown | Modelled BAC over time and each beverage's contribution to alcohol intake |
Practical Use Cases
Health educators: Illustrate how a fixed quantity of alcohol can produce different modelled BAC values when body weight or distribution factor changes.
Students: Explore how a Widmark-style dose estimate and a constant hourly elimination assumption shape a time-series graph.
Event organisers: Compare beverage quantities and strengths to explain how total pure-alcohol intake builds across different drink choices, without using estimates to assess anyone's fitness to travel.
Wellbeing coaches: Discuss the distinction between grams of alcohol, standard-drink totals and estimated BAC, and highlight why individual results vary.
Individuals tracking consumption: Itemise beverages, compare 10 g and 14 g standard-drink definitions and review approximate intake as an educational reference, not a sobriety test.
Accuracy and Limitations
This is a theoretical Widmark-based estimate, not a clinical BAC measurement. It assumes alcohol is spread evenly throughout the stated drinking period and removed at a constant rate; it does not model delayed absorption, food intake, changes in elimination, medicines, health conditions or person-to-person variation. Its peak-time estimate can be unrealistic, especially when drinking duration is zero or absorption is delayed; actual BAC may rise after drinking ends. The projected time to zero is not a safe-driving or decision-making threshold. Only an appropriate breath or blood test can measure alcohol concentration.
