BMR Calculator (Katch-McArdle Formula)
Calculate your Basal Metabolic Rate using the Katch-McArdle formula, which uses lean body mass for a more accurate estimate. Enter your body fat percentage directly or let us estimate it from your measurements.
What Is the Katch-McArdle Formula?
The Katch-McArdle formula is a method for estimating Basal Metabolic Rate (BMR) that is unique because it uses lean body mass (LBM) as its sole input variable. Unlike the Harris-Benedict or Mifflin-St Jeor equations that rely on total body weight, sex, age, and height, the Katch-McArdle approach accounts for body composition directly.
This makes it particularly valuable for:
- Athletes who carry significantly more muscle than average
- Bodybuilders with very low body fat percentages
- Anyone who knows their body fat percentage from DEXA scans, calipers, or BIA scales
Because the formula is based on lean mass, it applies equally to both men and women — no sex-specific variants are needed.
The Formula Explained
Where LBM = Total Body Weight × (1 − Body Fat Fraction)
For example, a person weighing 75 kg with 20% body fat:
- LBM = 75 × (1 − 0.20) = 75 × 0.80 = 60 kg
- BMR = 370 + (21.6 × 60) = 370 + 1,296 = 1,666 kcal/day
Understanding Lean Body Mass
Lean Body Mass (LBM) is everything in your body that is not fat — muscles, bones, organs, water, and connective tissue. It is the primary driver of metabolic rate because muscle tissue is metabolically active, burning calories even at rest.
| Component | Approximate % of LBM | Metabolic Activity |
|---|---|---|
| Skeletal muscle | ~50% | High — ~13 kcal/kg/day |
| Organs (liver, brain, heart, kidneys) | ~10% | Very High — 200–440 kcal/kg/day |
| Bone | ~15% | Low — ~2.3 kcal/kg/day |
| Water & other | ~25% | Minimal |
How to Measure Body Fat
| Method | Accuracy | Cost | Accessibility |
|---|---|---|---|
| DEXA scan | ±1–2% | $50–150 | Clinical settings |
| Hydrostatic weighing | ±1.5–2.5% | $40–100 | University labs |
| Bod Pod (air displacement) | ±2–3% | $40–75 | Fitness centers |
| Skinfold calipers | ±3–4% | $5–30 | At home / gym |
| BIA scales | ±3–5% | $20–200 | At home |
| US Navy method (circumferences) | ±3–4% | Free | At home |
| BMI-based estimation | ±5–8% | Free | At home |
If you don't know your body fat percentage, use our "Estimate" tab which calculates it from your age, sex, weight, and height using the BMI-based estimation method.
Cunningham Equation
The Cunningham equation is similar to Katch-McArdle but was designed specifically for athletes. It uses a slightly different constant:
The Cunningham equation tends to predict a slightly higher BMR, which may better reflect the elevated metabolism of regularly training athletes.
Katch-McArdle vs. Other BMR Formulas
| Formula | Inputs | Gender-Specific? | Best For |
|---|---|---|---|
| Katch-McArdle | LBM only | No | Anyone with known BF% |
| Cunningham | LBM only | No | Athletes |
| Harris-Benedict | Sex, Age, Weight, Height | Yes | General population |
| Mifflin-St Jeor | Sex, Age, Weight, Height | Yes | Overweight adults |
Calculating TDEE from BMR
| Activity Level | PAL Factor | Examples |
|---|---|---|
| Sedentary | 1.2 | Desk job, no exercise |
| Lightly Active | 1.375 | Walking, light gym 1–3x/week |
| Moderately Active | 1.55 | Moderate gym 3–5x/week |
| Very Active | 1.725 | Hard training 6–7x/week |
| Extra Active | 1.9 | Athletes, physical labor + training |
Accuracy & Best Use Cases
The Katch-McArdle formula is considered one of the most accurate BMR predictions when body fat percentage is known accurately. Studies show:
- Accuracy within ±3–5% when using DEXA-measured body fat
- Less accurate when body fat is estimated from BMI (±5–8% error in BF% estimate compounds)
- Excellent for muscular individuals where standard formulas overestimate (less muscle assumed)
- Excellent for high-body-fat individuals where standard formulas underestimate
Frequently Asked Questions
Why doesn't the Katch-McArdle formula use age or sex?
Age and sex affect BMR primarily through their influence on body composition — older people tend to have less muscle, and women tend to have more body fat than men at the same weight. Since the Katch-McArdle formula uses lean body mass directly, these factors are already accounted for indirectly.
Which is more accurate: Katch-McArdle or Harris-Benedict?
If you have an accurate body fat measurement, Katch-McArdle is generally more accurate because it accounts for body composition. Harris-Benedict can overestimate BMR in obese individuals and underestimate it in muscular individuals because it uses total weight rather than lean mass.
How do I estimate body fat without a DEXA scan?
Use our "Estimate Body Fat %" tab, which applies a BMI-based formula. For a more hands-on approach, use skinfold calipers (3–7 site methods) or the US Navy circumference method (neck + waist for men; neck + waist + hip for women).
Can this formula be used for children?
The Katch-McArdle formula was developed using adult data and is not validated for children or adolescents. For pediatric BMR estimation, use the Schofield equations or consult a pediatric dietitian.