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Distribution in Body
Volume of Distribution (Vd)
Fixed Vd Approach based on Sex at Birth
Individualized Vd Approach
Range of Values
TBW = total body water (L)
a = age (years)
h = height (cm)
w = weight (kg)
Vdmale = TBW /w x 0.825
±𝑉𝑑 𝑚𝑎𝑙𝑒 = 𝑉𝑑 ± (𝑉𝑑 × 9.86%)
Vdfemale = TBW / w x 0.838
±𝑉𝑑𝑓𝑒𝑚𝑎𝑙𝑒 = 𝑉𝑑 ± (𝑉𝑑 × 15.00%)
This Calculator is designed to permit lawyers to explore possible defences or prepare for crossexaminations. Don't use it to decide whether or not to drink and drive. It is dangerous to use these calculations to determine the ability to drive a vehicle or operate machinery after consuming alcohol. If you do so you assume full risk of legal prosecution, injury, illness, or death to yourself and others.
Drinking Scenario
Drink #1
Dose calculation in g
Scenario Summary
Drink #2
Dose calculation in g
Drink #3
Dose calculation in g
Total Dose calculation in g and number of standard drinks.
Subject's Body
Height Conversion 0 cm.
Weight Conversion 0 kg.
Notes:

The calculation uses Sex at Birth not gender.

Did you select a Unit of Height (inches or cm.) and a Unit of Weight (lbs. or kg.) ?

Do the height and weight conversions make sense?
Body Summary
Volume of Distribution (Vd)
Two Approaches: Fixed and Individualized
Fixed Vd Approach Based on Sex at Birth
If a fixed Vd range based on sex is used, 0.00 to 0.00 L/kg should be used.
Individualized Vd Approach Based on Sex at Birth, Age, Height, and Weight (3 steps):
Calculate TBW
Calculate Vd
Range of Values
1. Calculate TBW
TBW = total body water (L)
TBW is 0 L
Values Check for TBW calculation: TBWconstant is 0.0, ageconstant is 0.0, age is 0, heightconstant is 0.0, heightconversion is 0, weightconstant is 0, weightconversion is 0.
𝑇𝐵𝑊 (𝑚𝑎𝑙𝑒) = 2.447 − (0.09516 × 𝑎) + (0.1074 × ℎ) + (0.3362 × 𝑤) Equation (1a)
TBW = TBWconstant  (ageconstant × 𝑎ge) + (heightconstant × ℎeightconversion) + (weigtconstant × 𝑤eightconversion)
𝑇𝐵𝑊 (𝑓𝑒𝑚𝑎𝑙𝑒) = −2.097 + (0.1069 × ℎ) + (0.2466 × 𝑤) Equation (1b)
𝑇𝐵𝑊 = TBWconstant + (ageconstant (i.e. 0) x age) + (heightconstant × ℎeightconversion) + (weightconstant × 𝑤eightconversion)
TBW = TBWconstant + (ageconstant × 𝑎ge) + (heightconstant × ℎeightconversion) + (weigtconstant × 𝑤eightconversion)
Note the  or + after the TBW constant depends on sex at birth so the sign is switched in ageconstant for males, in order to consolidate the two TBW formulas into one, for both sexes at birth.
2. Calculate Individualized Vd
Vd = volume of distribution (L/kg)
Vd is 0 L/kg
𝑉𝑑 (𝑚𝑎𝑙𝑒) = TBW / (w x 0.825) Equation (2a)
𝑉𝑑 (𝑓𝑒𝑚𝑎𝑙𝑒) = TBW / (w x 0.838) Equation (2b)
3. Range of Values for Individualized Vd
Range is 0 to 0 L/kg
𝑉𝑑 (𝑚𝑎𝑙𝑒) = 𝑉𝑑 ± (𝑉𝑑 × 9.86%) Equation (3a)
𝑉𝑑 (𝑓𝑒𝑚𝑎𝑙𝑒) = 𝑉𝑑 ± (𝑉𝑑 × 15.00%) Equation (3b)
Time
Equation 4: Widmark's Formula
(full absorption and no elimination)
(similar to Equation 8)
𝐴𝐶 = D / Vd x w
where:
AC = alcohol concentration (g/L)
D = dose (g)
Vd = volume of distribution (L/kg)
w = weight (kg)
At your first interview with the new client, you should establish a starting point in time, Time 0, when:

the client started drinking,

and hopefully the client had a BAC of 0 when they started drinking,

and hopefully the client has some restaurant/bar receipts, or some other independent way of establishing that Time 0 through a witness, mobile phone record, or parking receipt.
For purposes of Equation 4, "Widmark's Formula", start by assuming that all of the Drinks were absorbed instantaneously into the subject Body at Time 0 with no elimination. You probably already know that absorption of the Drinks by the subject Body does not happen instantaneously, and the drinking scenario obviously happens over time. However, to estimate BAC (what the Equation calls "AC") at a later time you need to start somewhere. Specifically, you need to account for all of the Drinks being in the subject Body, use the basic Widmark Formula and then adjust. In reality, the AC concentration rises rapidly after consumption during the absorptive phase (some elimination is also taking place) and falls slowly during the postabsorptive phase (elimination only). In between those two phases, there is a plateau phase when the AC bounces up and down somewhat because both absorption and elimination are competing at the same time. The time of the incident is critical and as we know, the prosecutor sometimes has difficulty establishing that time. At the time of the incident, the subject Body may have been in the absorptive phase, the plateau phase, or in the postabsorptive elimination only phase.
I highly suggest that you join the DUIDLA and subscribe to Counterpoint Journal, if you have not already done so. Use their continuing education programs and videos to learn about absorption and elimination.
I have done my best to make this calculator userfriendly for both Criminal Lawyers Association members in Canada and DUIDLA members in the United States and Canada. Please indicate below whether you wish to use the original Widmark formula units g/L, the US units g/dL, or the Canadian units mg/100mL for purposes of Equation 4. If you decide to do Retrograde Extrapolation Equations 9 or 10, or Equations 5 or 6 calculations, please be consistent in using US or Canadian units.
Scenario Summary
Body Summary
Vd Summary
Widmark and Time Summary
Possible Errors in Units: Please be careful to be consistent to use the same USA g/dL or Canada mg/100mL units in all areas of this calculator. The Widmark g/L unit is used by some experts. You will need to make this choice in both this red Section and the green Retrograde Analysis Section.
Possible Error Messages: NaN means "Not a Number". "Infinity"is not a good AC calculation. Vd ranges above 1.0 L/kg or a negative Vd number indicate an error. If you receive one of these errors please check to make sure you have entered at least one drink in the Drinks section and all the inputs in the Body section.
Adjust for Incomplete Absorption
(Use the Slider to Adjust Percentage Absorption)
Before Elimination but After Any Absorption Adjustment 🧽
AC (Fixed Vd) Range is 0 to 0
AC (Individualized Vd) Range is 0 to 0
Adjust for Elimination Rate During Time Between Start of First Drink and the Incident
(Use the Slider to Adjust the Elimination Rate)
Elimination 0
After Elimination 🚽
AC (Fixed Vd) Range is 0 to 0
AC (Individualized Vd) Range is 0 to 0
Units
Retrograde Extrapolation and Adjustments
Equations 9 and 10
Retrograde Extrapolation (if subject postabsorptive at time of incident)
Equation (9)
𝐴𝐶inc = where:
ACinc = ACtest + (𝛽 x T)
where:
𝐴𝐶inc = estimated alcohol concentration at the time of the incident (g/dL)
ACtest = measured alcohol concentration (g/dL)
𝛽 = elimination rate (0.0100.025 g/dL/hour)
T = time between incident and time of breath test/blood draw (hours)
Retrograde Extrapolation Summary
AC at time of incident is 0 to 0
Units
If the drinking scenario indicates unabsorbed alcohol at the time of the incident, or there is evidence of post incident alcohol consumption, the next step is to subtract the impact of those drinks from the estimated post absorptive alcohol range of concentrations.
Equation (10)
Adjusted ACinc = ACinc – ACdrink(s) where:
Adjusted ACinc = estimated AC at time of the incident, accounting for potentially unabsorbed alcohol or post incident alcohol consumption
ACinc = estimated AC at time of the incident if subject were in post absorptive state (calculated from Equation 9)
ACdrink(s) = maximum AC contribution from drink(s) (calculated from Equation 8)
Warning: This subtraction can result in lots of errors so it is ripe for crossexamination. Watch for errors in your own calculation and in calculations made by experts:

Incomplete information or data entry as to sex at birth, age, height, and weight. Fixed Vd calculations require data entry of weight, weight units, and sex at birth. Individualized Vd calculations additionally require data entry of age, height, and height units.

Errors related to data entry of ounces v. mLs, inches v. cm.

Errors or confusion of decimals among g/L, g/dL, and mg/100mL.
To manually subtract an unabsorbed drink or a post incident drink using Equations 7, 8, 9, and 10, enter the unabsorbed or post incident adjustment drink volume and concentration below , enter subject sex at birth, (age, height  if you are calculating individualized Vd), and weight in the Body section of this page, select the Unit of Alcohol Concentration (US or Canada units) in the green section above, read the two ranges of adjustment below, and subtract the following from the Retrograde Extrapolation Equation 9 AC range calculation. Warning: It very easy to err in making this calculation. Read the data entry summaries below to make sure they match your unabsorbed drink or post incident drink scenario only. Individualized Vd calculations will not work properly unless you have entered all Body fields including age and height.
Did you select a "Unit of Alcohol Concentration for Retrograde Extrapolation" (green section) above to ensure that results are stated correctly in g/dL or mg/100mL?
Did you enter data for this person's body in the Body (brown) section above?
AC Drink(s): Unabsorbed Drink or PostIncident Drink
Widmark unit and ACunit
ACdrinks calculation of dose
ACdrink(s) (Fixed Vd) Range is 0 to 0
ACdrink(s) (Individualized Vd) Range is 0 to 0
Units
Body Summary
Retrograde Extrapolation Summary
Use these Equations to Destroy the Evidence of the Accused as to Drinking Scenario:
Theoretical Minimum Number of Drinks
Equation 5 Minimum dose (in g) of alcohol to achieve a particular alcohol concentration in the body of this Accused.
Equation 6 Minimum number of “drinks” to achieve that dose when the Accused has given evidence of a type of beverage with a known concentration.
THIS CALCULATOR WILL NOT WORK PROPERLY UNLESS YOU HAVE SPECIFIED US g/dL OR CANADIAN mg/100 mL UNITS IN THE RETROGRADE EXTRAPOLATION GREEN SECTION ABOVE
Units of AC for Equations 5 and 6 are the same as Equations 9 (and 10) "Unit of Alcohol Concentration for Retrograde Extrapolation"
Equation 5 summary
Body Summary
Vd Summary
(Equation 5 2024) Calculation of Minimum Dose of Alcohol to Produce a Concentration
(5) 𝐷 (in g) =𝐴𝐶 × 𝑉𝑑 × 𝑤 × 10 dL/L (in US)
where:
D = dose (g)
AC = alcohol concentration (g/dL)
Vd= volume of distribution (L/kg)
w= weight (kg)
Use of this equation requires input of an alcohol concentration determined by blood draw or breath test as well as input of data (to calculate Vd) as to sex at birth, age, height in inchesor cm and weight in lbs. or kg.
Use the inputs in the "Body" section of this page to calculate both fixed Vd ranges and individualized Vd ranges.
Using Equation 5, calculate with a fixed Vd range: AC x Vd L/kg (minimum and maximum) x w kg x 10 (dL/L in US) = Dose in g
Using Equation 5 calculate with an individualized Vd range: AC x Vd L/kg (minimum and maximum) x w kg x 10 (dL/L in US) = Dose in g
Dose in g can them be converted into the minimum number of "drinks" when the concentration is known. Use Equation 6.
(Equation 6 2024) Dose in g converted into the minimum number of "drinks" when the concentration is known.
V = D / (C x p x m)
where:
V = Volume in oz.
D = Dose in g.
C = Beverage concentration mL/100mL
p = Density of ethanol 0.789 g/mL
m = metric conversion 29.6 ml/oz.
Use of this equation requires prior calculation of Dose and data input of Concentration of the "drinks". In the US a "standard drink" is a beverage containing 14 grams of ethyl alcohol:
12 US oz, 5% beer
5 US oz, 12% wine
1.5 US oz, 80 proof liquor (40%)
Using Equation 6, calculate V in US oz. with a fixed Vd range: Dose 0 g / (Concentration of the Beverage .000 ethyl alcohol x p .789 g/mL x metric conversion in US) = Volume measured in the following size units or glasses.
Using Equation 6 calculate V in US oz. with an individualized Vd range: Dose 0 g / (Concentration of the Beverage .000 ethyl alcohol x p .789 g/mL x metric conversion in US) = Volume measured in the following size units or glasses.
Equation Summary Array
Glass Volume Conversion
Warning: Use of equations 5 and 6 can result in lots of errors so they are ripe for crossexamination and rebuttal evidence. They assume the evidentiary breath test result or blood draw result is reliable. It may not be. Watch for errors in your own calculation and in calculations made by experts:

Incomplete information or data entry as to sex at birth, age, height, and weight. Fixed Vd calculations require data entry of weight, weight units, and sex at birth. Individualized Vd calculations additionally require data entry of age, height, and height units.

Errors related to data entry of ounces v. mLs, inches v. cm.

Errors or confusion of decimals among g/L, g/dL or g/210L, and mg/100mL.
List of Equations in ANSI/ASB Best Practice Recommendation 122, 1st Ed. 2024:
(Equation 1 2024) Calculate Total Body Water (TBW) from Watson, et al :
(1a) 𝑇𝐵𝑊 (𝑚𝑎𝑙𝑒) = 2.447 − (0.09516 × 𝑎) + (0.1074 × h) + (0.3362 × 𝑤)
(1b) 𝑇𝐵𝑊 (𝑓𝑒𝑚𝑎𝑙𝑒) = −2.097 + (0.1069 × h) + (0.2466 × 𝑤)
(Equation 2 2024) Calculate the individualized Volume of Distribution (Vd) from Maskell, et al:
(2a) 𝑉𝑑 (𝑚𝑎𝑙𝑒) = TBW / (w x 0.825)
(2b) 𝑉𝑑 (𝑓𝑒𝑚𝑎𝑙𝑒) = TBW / (w x 0.838)
See ANSI/ASB 2024 footnotes 16, 19
(Equation 3 2024) Apply the ± %CV from Maskell, Cooper:
(3a) 𝑉𝑑 (𝑚𝑎𝑙𝑒) = 𝑉𝑑 ± (𝑉𝑑 × 9.86%)
(3b) 𝑉𝑑 (𝑓𝑒𝑚𝑎𝑙𝑒) = 𝑉𝑑 ± (𝑉𝑑 × 15.00%)
See ANSI/ASB 2024 footnote 16
(Equation 4 2024) Widmark’s Formula:
𝐴𝐶 = D / Vd x w
Use of this equation requires input of data as to sex at birth, age, height in inches or cm, and weight in lbs. or kg. and requires input of data as to Dose which is calculated by input of data repecting volume of drink in mL. or oz. and concentration of ethyl alcohol in the drink.
(Equation 5 2024) Calculation of Minimum Dose of Alcohol to Produce a Concentration
(5) 𝐷 (in g) =𝐴𝐶 × 𝑉𝑑 × 𝑤 × 10 dL/L (in US)
where:
D = dose (g)
AC = alcohol concentration (g/dL)
Vd= volume of distribution (L/kg)
w= weight (kg)
Use of this equation requires input of an alcohol concentration determined by blood draw or breath test as well as input of data (to calculate Vd) as to sex at birth, age, height in inchesor cm and weight in lbs. or kg.
Use the inputs in the "Body" section of this page to calculate both fixed Vd ranges and individualized Vd ranges.
Dose in g can them be converted into the minimum number of "drinks" when the concentration is known. See Equation 6.
(Equation 6 2024) Dose in g converted into the minimum number of "drinks" when the concentration is known.
V = D / (C x p x m)
where:
V = Volume in oz.
D = Dose in g.
C = Beverage concentration mL/100mL
p = Density of ethanol 0.789 g/mL
m = metric conversion 29.6 ml/oz.
Use of this equation requires prior calculation of Dose and data input of Concentration of the "drinks". In the US a "standard drink" is a beverage containing 14 grams of ethyl alcohol:
12 US oz, 5% beer
5 US oz, 12% wine
1.5 US oz, 80 proof liquor (40%)
(Equation 7 2024) Dose of alcohol from a drink
𝐷= 𝑉 ×𝐶 × ρ × 𝑚
where:
V = Volume in oz.
D = Dose in g.
C = Beverage concentration mL/100mL
p = Density of ethanol 0.789 g/mL
m = metric conversion 29.6 ml/oz.
(Equation 8 2024) Theoretical maximum alcohol concentration from a given drink(s), Widmark formula with 100% absorption and no elimination
𝐴𝐶 = D / Vd x w x 10 dL/L in US [note the similarity to Equation 4]
where:
AC = alcohol concentration (g/L)
D = dose (g)
Vd = volume of distribution (L/kg)
w = weight (kg)
(Equation 9 2024) Retrograde Extrapolation
𝐴𝐶inc = where:
ACinc = ACtest + (𝛽 x T)
where:
𝐴𝐶inc = estimated alcohol concentration at the time of the incident (g/dL)
ACtest = measured alcohol concentration (g/dL)
𝛽 = elimination rate (0.0100.025 g/dL/hour)
T = time between incident and time of breath test/blood draw (in hours)
(Equation 10 2024) Adjustment to Retrograde Extrapolation for Unabsorbed Alcohol or Postincident Alcohol Consumption
Adjusted ACinc = ACinc – ACdrink(s) where:
Adjusted ACinc = estimated AC at time of the incident, accounting for potentially unabsorbed alcohol or post incident alcohol consumption
ACinc = estimated AC at time of the incident if subject were in post absorptive state (calculated from Equation 9)
ACdrink(s) = maximum AC contribution from drink(s) (calculated from Equation 8)
Problems (under construction I have colour coded the data input areas in this calculator):
A.1 Support/refute drinking history
Male sex at birth
73 inches height
230 lbs. weight
Age 32
Evidentiary Breath Test 0.19
g/210L
Brand X Beer .043 concentration
Pints US 16 oz.
Quantity 2
A.1.1 What is the minimum number of drinks needed to reach a 0.19 g/210 L alcohol concentration?
[To use this calculator, you will primarily enter data and use results in the orange Crown crossexamination section, but you will also need to input data (and verify Vd calculations) in the brown Body section and clarify US or Canadian units inthe green Thinking Backwards section.]
a) Calculate with a fixed Vd range
Using Equation 5 calculate the dose needed to reach that AC
Using Equation 6, calculate the equivalent number of drinks for that dose
b) Calculate with an individualized Vd range
Using Equation 1a, calculate the TBW
Using Equation 2a, calculate the Individualized Vd
Using Equation 3a, apply the %CV
Using Equation 5 and an Individualized Vd range of L/kg, calculate the dose needed to reach that AC
Using Equation 6, calculate the equivalent number of drinks for that dose
A.1.2 What is maximum AC that could be reached from 2 pints of Brand X beer?
Male sex at birth
73 inches height
230 lbs. weight
Age 32
Assume:
Evidentiary Breath Test 0.19
US units (Enter both places for consistency):
g/210L
and
US units (Enter both places for consistency):
g/210L
Accused states (My preference):
Brand X Beer .043 concentration
Pints US 16 oz.
Quantity 2 = 32 oz.
or
Accused states (Best Practices):
Brand X Beer .043 concentration
Pints US 16 oz.
Quantity 2 = 32 oz.
[The Best Practices advise using Equation 8 (theoretical max) but I prefer to use Equation 4 (the Widmark formula) . Either approach should work.]
Using Equation 7, (Best Practices approach) calculate the dose from 2 pints of Brand X beer
I would use Equation 7 (my approach)
a) Calculate with a fixed Vd range
b) Calculate with an individualized Vd range
A.2 Retrograde extrapolation, subject is post absorptive
Female sex at birth
63 inches height
125 lbs. weight
Age 45
Blood Test 0.068 @ 23:45
Incident @ 21:00
Elapsed Time calculation 2.75 hours
3 hours between the end of drinking and the incident
No post incident alcohol consumption
g/dL
A.3 Retrograde extrapolation, subject is not post absorptive
Female sex at birth
68 inches height
160 lbs. weight
Age 22
Blood Test 0.082 @ 00:30
Incident @ 23:00
Elapsed Time calculation 1.5 hours
g/dL
Accused states:
Stopped main drinking scenario 22:00
Last Drink: Tequila .40 concentration
Shot US 1.5 oz.
@23:00
Using Equation 7 calculate the dose of alcohol from the Last Drink shot.
Using Equations 1b, 2b, and 3b, calculate an individualized Vd range.
A.4 Post Incident Consumption
Male sex at birth
70 inches height
210 lbs. weight
Age 55
Assume:
Evidentiary Breath Test 0.215
Drove through garage door @ 18:00
US units:
g/210L
Accused states:
No predriving alcohol
Vodka .40 concentration, 750 ml. bottle 1/3 empty
Postdriving consumption 250 ml.
Using Equation 7, calculate the dose of alcohol consumed postdriving.
Using Equations 1b, 2b, and 3b, calculate an individualized Vd range.
A.5 Minimal Case History Available
Female sex at birth
Unknown height
160 lbs. weight
Age unknown
Blood Test 0.075 @ 03:00
Incident @ 01:00
Elapsed Time calculation 2.0 hours
US units:
g/dL
Use “Standard” drink = 14 g of alcohol