How to Calculate BAC

Understanding the factors that affect your Blood Alcohol Content

BAC Formula

BAC = (Alcohol in grams × 100) ÷ (Weight in grams × Gender Constant) - (0.015 × Hours)

Key Factors:

  • Weight: Heavier people have lower BAC
  • Gender: Women generally have higher BAC
  • Alcohol consumed: Standard drinks (14g alcohol each)
  • Time: Alcohol metabolizes at ~0.015% per hour

Example BAC Calculation

For someone who is:

  • Weight: 70 kg (male)
  • Drinks: 3 standard drinks
  • Time: 2 hours since first drink

1. Alcohol = 3 × 14g = 42g

2. BAC = (42 × 100) ÷ (70 × 0.68) - (0.015 × 2)

3. BAC = 0.064%

This BAC of 0.064% indicates mild impairment.

Standard Drink Equivalents

Beer

  • • 12 oz (355 ml)
  • • 5% alcohol
  • • 1 standard drink

Wine

  • • 5 oz (148 ml)
  • • 12% alcohol
  • • 1 standard drink

Spirits

  • • 1.5 oz (44 ml)
  • • 40% alcohol
  • • 1 standard drink

Important Safety Information

Time Matters

Your body processes alcohol at about one standard drink per hour

Know Your Limits

Legal limit is 0.08% in most places, but impairment starts much lower

Plan Ahead

Always arrange for a designated driver or alternative transportation