Mifflin-St Jeor Equation Step by Step Guide
The Mifflin-St Jeor Equation is universally considered by dietitians and medical professionals to be the most accurate formula for estimating a human's Basal Metabolic Rate (BMR)-the number of calories burned while at complete rest.
Developed in 1990 by MD Mifflin and ST St Jeor, this formula improved upon older equations (like the Harris-Benedict equation) by accounting for modern population body composition.
This guide details the step-by-step mathematical calculations for men and women using our BMR Calculator.
The Mifflin-St Jeor Equations
Variables required:
- $W$ = Weight in kilograms ($\text{lbs} \div 2.2046$)
- $H$ = Height in centimeters ($\text{inches} \times 2.54$)
- $A$ = Age in years
Formula for Men:
$$\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) + 5$$
Formula for Women:
$$\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) - 161$$
Worked Calculation Example (Female)
Calculate BMR for a 35-year-old woman weighing 65 kg (143 lbs) with a height of 165 cm (5 ft 5 in):
Step 1: Multiply Weight ($10 \times W$)
$$10 \times 65 = 650$$
Step 2: Multiply Height ($6.25 \times H$)
$$6.25 \times 165 = 1031.25$$
Step 3: Multiply Age ($5 \times A$)
$$5 \times 35 = 175$$
Step 4: Apply Formula with Female Constant (-161)
$$\text{BMR} = 650 + 1031.25 - 175 - 161 = \mathbf{1,345.25 \text{ kcal / day}}$$
At complete bed rest, her body requires approximately 1,345 calories per day to sustain vital organ functions.
BMR vs Total Daily Energy Expenditure (TDEE)
BMR does not account for physical activity. To calculate total daily calorie needs (TDEE), multiply BMR by an activity factor:
- Sedentary (Desk Job): $\text{BMR} \times 1.2$
- Lightly Active (1-3 days/wk exercise): $\text{BMR} \times 1.375$
- Moderately Active (3-5 days/wk exercise): $\text{BMR} \times 1.55$
Automate Your BMR & Macro Calculations
Calculate your exact BMR and daily caloric needs using our free BMR Calculator and TDEE Calculator. Explore more tools in our Health & Fitness Category.
For a comparison of metabolic formulas, see Mifflin vs Harris Benedict TDEE Formula.
