This estimator applies the Widmark equation — the same model used in toxicology research — to predict blood-alcohol concentration from drinks consumed, body weight, sex, and time. It is for education only. Texas DWI cases are proven by breath or blood test results (Tex. Penal Code § 49.04), not estimates. Do not drive after drinking.
Enter drinks consumed, weight, sex, and hours since first drink. Results update live.
The Widmark equation
The Widmark equation, developed by Swedish physician Erik M. P. Widmark in 1932, estimates BAC from alcohol consumed and body composition. The formula: BAC = (alcohol_grams ÷ (weight × r)) − (β × hours), where r is the distribution factor (~0.68 for men, ~0.55 for women, reflecting differences in total body water) and β is the elimination rate (~0.015 BAC/hour average). Both variables have wide individual variation.
The equation has stood for nearly a century because the underlying physiology is simple: alcohol distributes through the body's water compartment, and the liver metabolizes it at a roughly steady rate. What makes the equation a poor predictor for any specific person is the input variability — actual r in a healthy adult ranges from 0.55 to 0.85 in men and from 0.49 to 0.65 in women, and actual elimination rate ranges from 0.010 to 0.020 BAC/hour depending on liver enzyme expression and chronic-drinking adaptation.
What a "standard drink" is
A U.S. standard drink contains 14 grams of pure ethanol. The equivalents:
Beverage
Volume
ABV
Grams alcohol
Beer (light to standard)
12 oz
5%
14 g
Beer (craft / high-ABV)
12 oz
7–9%
20–26 g (1.4–1.9 standard drinks)
Wine
5 oz
12%
14 g
Wine (typical restaurant pour)
6–7 oz
13–14%
17–20 g (1.2–1.4 standard drinks)
Spirits (80-proof)
1.5 oz
40%
14 g
Spirits (cocktail with 2 oz)
2 oz
40%
19 g (1.4 standard drinks)
Spirits (heavy pour cocktail)
3 oz
40%
28 g (2 standard drinks)
The estimator assumes 14g per drink. If you had a 32-oz light beer, that's ~2.7 standard drinks. A martini at a restaurant is often 2-3 standard drinks. Reported drink count systematically understates alcohol intake.
Texas BAC thresholds
BAC range
Texas legal status
Citation
0.00 – 0.07
Below per-se DWI threshold (but loss-of-faculties DWI still possible)
Tex. Penal Code § 49.01(2)
0.04 – 0.07
Per-se DWI threshold for commercial drivers operating a commercial vehicle
Tex. Transp. Code § 522.101
0.08 – 0.14
Per-se DWI (Class B misdemeanor for first offense)
Tex. Penal Code § 49.04
0.15 and above
Class A misdemeanor for first-offense DWI (elevated punishment)
Tex. Penal Code § 49.09(d)
Any BAC, driver under 21
Class C DUI by Minor (zero-tolerance)
Tex. Alc. Bev. Code § 106.041
Why estimates are not actual BAC
Even with accurate inputs, a Widmark-equation BAC estimate can be 30-50% off the actual breath or blood test result for these reasons:
Individual r varies widely. Body composition matters more than weight alone. Athletes and lean people have higher r; people with more body fat have lower r.
Elimination rate varies. Heavy chronic drinkers eliminate faster (up to 0.025 BAC/hour); infrequent drinkers eliminate slower. Liver disease, certain medications, and age all affect rate.
Absorption is not instant. Peak BAC occurs 30-90 minutes after the last drink, depending on stomach contents. The equation assumes peak immediately.
Food intake. Eating slows absorption and lowers peak. The equation does not adjust.
Drink reporting is inaccurate. Most people under-report drinks and underestimate pour sizes.
Time-of-last-drink matters. The estimator assumes all drinks were consumed at hour 0. Spreading drinks over time shifts the curve.
Why estimates are not a DWI defense
An estimated BAC has no evidentiary value in a Texas DWI trial. The State proves BAC with a breath test (Intoxilyzer 9000) or a blood test. The defense challenges that actual test result by attacking:
Calibration and maintenance records for the testing instrument
Operator certification and procedural compliance with Texas DPS Forensic Services rules
Expert testimony on extrapolation back to the time of driving (the test is usually 30+ minutes after the stop)
Retrograde extrapolation challenges — drinking on an empty stomach with rising BAC can mean BAC at driving was lower than at the test
A Widmark estimate does not move the needle in any of these attack vectors.
DWI at BAC below 0.08
Texas DWI is defined two ways under § 49.01(2). The per-se prong (B) requires BAC ≥ 0.08. The loss-of-faculties prong (A) requires showing that the defendant did not have the normal use of mental or physical faculties due to alcohol, drugs, or any combination. The State only needs to prove ONE prong to convict.
The loss-of-faculties prong has no BAC requirement. A defendant who fails field-sobriety tests at BAC 0.04 can be convicted. Officers are trained to observe and document indicia of intoxication (slurred speech, bloodshot eyes, balance problems, divided-attention failures on field sobriety tests) that work as evidence regardless of BAC.
Cite this calculator
L and L Law Group, BAC Estimator, landllawgroup.com/bac-estimator/ (last updated May 16, 2026).
Frequently asked questions
What is the legal BAC limit for DWI in Texas?
0.08 for drivers 21+ operating a non-commercial vehicle under Tex. Penal Code § 49.01(2)(B). Commercial drivers operating a commercial vehicle have a 0.04 limit. Drivers under 21 face zero tolerance — any detectable amount is a Class C DUI under Alc. Bev. Code § 106.041.
How accurate is a BAC estimator?
Not very. Widmark estimates can be 30–50% off actual breath or blood test results. Individual variation in distribution factor, elimination rate, absorption time, and pour-size accuracy means estimates should be treated as rough educational guides only.
Can I use a BAC estimator as a defense to a DWI?
No. Texas DWI is proven by either (1) per-se BAC ≥ 0.08 from breath or blood test, or (2) loss of normal faculties under § 49.01(2)(A). An estimated BAC has no evidentiary value at trial. Defense challenges target the actual test result through calibration, chain-of-custody, and procedural attacks.
What is the Widmark equation?
The Widmark equation, from Swedish physician Erik M. P. Widmark (1932), estimates BAC: BAC = (alcohol_grams / (weight × r)) − (β × hours). r is the distribution factor (0.68 male, 0.55 female average). β is elimination rate (~0.015 BAC/hr). Both have wide individual variation.
How long does alcohol stay in your system?
Roughly 1 hour to eliminate one standard drink. The body metabolizes at about 0.015 BAC per hour. A 0.08 BAC takes ~5.3 hours to reach zero. Eating, coffee, and exercise do not measurably speed elimination.
What is a standard drink?
14 grams of pure alcohol in the U.S. Equivalents: 12 oz beer at 5% ABV, 5 oz wine at 12% ABV, 1.5 oz of 80-proof spirits. Craft beers, large pours, and mixed drinks frequently contain 1.5–3 standard drinks per serving.
Why is BAC 0.15 significant in Texas?
§ 49.09(d) elevates DWI 1st from Class B misdemeanor to Class A (max 1 year jail, $4,000 fine) when BAC is 0.15+. The § 709 fine also doubles from $3,000 to $6,000.
Can I be convicted of DWI in Texas at BAC under 0.08?
Yes. § 49.01(2) defines DWI two ways: (A) loss of normal mental or physical faculties, OR (B) BAC ≥ 0.08. A defendant failing field-sobriety tests at BAC 0.05 can be convicted under the loss-of-faculties prong.
What is the BAC limit for commercial drivers in Texas?
0.04 when operating a commercial vehicle under Tex. Transp. Code § 522.101. First offense at 0.04 disqualifies CDL for 1 year. Second offense = lifetime disqualification. The 0.04 limit only applies when operating a commercial vehicle; in a personal vehicle the 0.08 limit applies.
Does eating before drinking lower your BAC?
Eating slows absorption, so peak BAC is lower and reached later. Food does not reduce total alcohol metabolized — the same drinks produce the same total exposure. The Widmark equation does not adjust for food intake.
How does sex affect BAC?
Women on average reach higher BAC than men at the same alcohol intake and weight. Lower distribution factor (~0.55 vs ~0.68, reflecting less total body water relative to weight) and lower stomach alcohol dehydrogenase mean less pre-absorption breakdown.
Do I have to take a breath or blood test in Texas?
You can refuse, but refusal triggers automatic 180-day ALR suspension on first refusal (2 years with prior alcohol contact) under Transp. Code Ch. 724. Refusal can also be introduced at trial. A warrant for blood draw is routinely sought after refusal.
Njeri M. London, Esq. is a Co-Founding Partner of L and L Law Group, PLLC in Frisco, Texas. She represents clients in DWI, drug, assault, federal, juvenile, and expunction matters across Dallas, Collin, Denton, and Tarrant counties. State Bar of Texas #24043266. Admitted in TXND, TXED, and the Fifth Circuit. Editorial review by Reggie London (Bar #24043514, former Dallas County ADA).