# HALP!! BAC Calculation **URL:** \ **Category:** Factual Questions\ **Created:** [November 14, 2009, 9:38am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541 "2009-11-14T09:38:36Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![bengangmo](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@bengangmo](https://boards.straightdope.com/u/bengangmo)\ **Post date:** [November 14, 2009, 9:38am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/1 "2009-11-14T09:38:36Z")
I need a factual answer and fast please please please (this is for an anti drink drive article in a magazine) I know that alcohol is metablised at the rate of 0.015% BAC per hour I also know that one standard drink = 0.02% BAC The legal limit is 35 microgrammes of alcohol per 100 millitres of breath, or more than 80 milligrammes of alcohol per 100 millitres of blood. So my question is - how do I convert from BAC to microgrammes / milligrammes per litre? ---
**Author:** ![bengangmo](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@bengangmo](https://boards.straightdope.com/u/bengangmo)\ **Post date:** [November 14, 2009, 9:39am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/2 "2009-11-14T09:39:36Z")
The intent of the question? Tell people how long they have to wait once they go over the limit, and how quickly they will get to the limit ---
**Author:** ![groman](https://avatars.discourse-cdn.com/v4/letter/g/73ab20/32.png) [@groman](https://boards.straightdope.com/u/groman)\ **Post date:** [November 14, 2009, 10:11am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/3 "2009-11-14T10:11:52Z")
> [@bengangmo](#): > > I also know that one standard drink = 0.02% BAC I think any kind of even rough metric that is “Amount of alcohol ==\> BAC” is not very useful at all. If you want a usable average try finding some sort of an average “Amount of alcohol/pound of body weight ==\> BAC” table. ---
**Author:** ![bengangmo](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@bengangmo](https://boards.straightdope.com/u/bengangmo)\ **Post date:** [November 14, 2009, 10:52am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/4 "2009-11-14T10:52:28Z")
> [@groman](#): > > I think any kind of even rough metric that is “Amount of alcohol ==\> BAC” is not very useful at all. If you want a usable average try finding some sort of an average “Amount of alcohol/pound of body weight ==\> BAC” table. I have found that - I have all the tables I need, but they are in BAC - I just don’t know how to get from BAC to microgrammes per milli-litre I am reasonably competent at math, and if I can get a straight forward formula I can do the math - just need a clear formula ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [November 14, 2009, 11:41am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/5 "2009-11-14T11:41:27Z")
1% BAC = 1/100 (%) g/mL = 1 cg/mL which would be 10,000 micrograms per ml. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [November 14, 2009, 11:45am UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/6 "2009-11-14T11:45:44Z")
Deleted. ---
**Author:** ![bengangmo](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@bengangmo](https://boards.straightdope.com/u/bengangmo)\ **Post date:** [November 14, 2009, 1:49pm UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/7 "2009-11-14T13:49:31Z")
> [@don\_t\_ask](#): > > 1% BAC = 1/100 (%) g/mL = 1 cg/mL which would be 10,000 micrograms per ml. Thanks man Hugely appreciated - I can work it out from here ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [November 14, 2009, 3:07pm UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/8 "2009-11-14T15:07:22Z")
Double post… ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [November 14, 2009, 3:10pm UTC](https://boards.straightdope.com/t/halp-bac-calculation/517541/9 "2009-11-14T15:10:37Z")
> [@don\_t\_ask](#): > > 1% BAC = 1/100 (%) g/mL = 1 cg/mL which would be 10,000 micrograms per ml. That’s not quite right. You’re comparing mass and volume. 1% would be 10,000 micrograms per _gram_, not mL. You need to factor in for the density of blood. Edit: Thinking about it though, it would be really close since blood is mostly water and the density of water is 1 g/mL. So depending on how accurate it needs to be, I guess this might work.