I've had a PM regarding drink driving in France - I thought it worth repeating my response here.
It's sometimes suggested that the French are relaxed about drink driving - but the truth is that in general the police operate a policy of zero tolerance of drink driving.
In order not to violate the law, your blood alcohol level while driving must be less than 0.5 grams of alcohol per litre of blood (or 0.25mg per litre of expired air).
A rule of thumb
The best thing is not to drink alcohol at all when driving. However, as a rule of thumb, and in no way to be taken as a recommendation or legal advice, an average (12 stone, 160-170 lb) man's limit in France is often quoted as two SMALL glasses of the type SERVED IN BARS AND RESTAURANTS AS STANDARD MEASURES. Those served in homes are generally much larger.
Each glass is equivalent to approx. 10g of alcohol, and once absorbed = approx 0.25 g of alcohol per litre of blood for a man of average build.
If you drink a standard French glass of beer (25 cl at 5°), wine (12.5cl at 10° to 12°) or whisky (3cl at 40 °), the amount of alcohol is roughly the same: 0.25 g of alcohol per litre of blood.
Smaller men and women will be over the limit after 2 glasses.
The body gets rid of alcohol at the rate of about 10g per hour (so gets rid of one standard glass in about 2.5 hours).
You can buy alcotests at pharmacies to check your own level.
Penalties:
Between 0.5 g and 0.8 g of alcohol per litre of blood, you are committing a "violation of the 4th class" with a fixed penalty of six points and fine of 135€. I don't know how the points part is dealt with for non-residents on foreign licences.
Over 0.8 g of alcohol per litre of blood, you are committing a crime and will have to appear in court. The court may order a fine of up to €4500, two years imprisonment, and a licence suspension up to three years.
Phil