What is BMR and what does it measure?

Basal Metabolic Rate (BMR) is the number of kilojoules your body needs to perform basic life-sustaining functions like breathing, circulation, cell production, and nutrient processing. It is measured at complete rest, in a fasted state, and in a thermally neutral environment.

What is the difference between BMR and TDEE?

BMR is the energy your body uses at complete rest. TDEE (Total Daily Energy Expenditure) includes your BMR plus the energy used for daily activities, exercise, and digesting food. TDEE is typically 1.2 to 1.9 times your BMR depending on how active you are.

Why is the Mifflin-St Jeor equation preferred?

The Mifflin-St Jeor equation (1990) has been shown in multiple studies to be the most accurate BMR prediction equation for most healthy adults, estimating BMR within 10% for about 80% of people. It is more accurate than the older Harris-Benedict equation.

Can I eat below my BMR?

Eating below your BMR is generally not recommended without medical supervision. Your body needs at least this much energy for basic functions. Sustained intake below BMR can trigger metabolic adaptation, muscle loss, and hormonal disruptions. Aim for a calorie target between your BMR and TDEE.

BMR Calculator

Calculate your Basal Metabolic Rate (BMR) — the number of kilojoules your body burns at complete rest just to keep you alive. BMR accounts for 60-75% of your total daily energy expenditure and is the foundation for calculating your calorie needs.

Enter Your Details

Gender

Age

years

Weight

Height

How It Works

BMR is calculated using the Mifflin-St Jeor equation, which is widely considered the most accurate formula for estimating resting energy expenditure. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. The result in kcal is then converted to kJ by multiplying by 4.184.

Quick Reference

Profile	Weight	Height	Age	BMR (kJ)	BMR (kcal)
Small female	50 kg	155 cm	25	5,071	1,212
Average female	65 kg	165 cm	30	5,778	1,381
Larger female	85 kg	170 cm	40	6,477	1,548
Small male	60 kg	165 cm	25	6,292	1,504
Average male	75 kg	175 cm	30	7,095	1,696
Larger male	95 kg	180 cm	35	7,978	1,907
Active female	60 kg	170 cm	28	5,862	1,401
Active male	80 kg	180 cm	28	7,578	1,812
Older female	70 kg	160 cm	55	5,519	1,319
Older male	80 kg	172 cm	55	6,590	1,575

BMR values calculated using the Mifflin-St Jeor equation.

Frequently Asked Questions

What is BMR and what does it measure?: Basal Metabolic Rate (BMR) is the number of kilojoules your body needs to perform basic life-sustaining functions like breathing, circulation, cell production, and nutrient processing. It is measured at complete rest, in a fasted state, and in a thermally neutral environment.
What is the difference between BMR and TDEE?: BMR is the energy your body uses at complete rest. TDEE (Total Daily Energy Expenditure) includes your BMR plus the energy used for daily activities, exercise, and digesting food. TDEE is typically 1.2 to 1.9 times your BMR depending on how active you are.
Why is the Mifflin-St Jeor equation preferred?: The Mifflin-St Jeor equation (1990) has been shown in multiple studies to be the most accurate BMR prediction equation for most healthy adults, estimating BMR within 10% for about 80% of people. It is more accurate than the older Harris-Benedict equation.
Can I eat below my BMR?: Eating below your BMR is generally not recommended without medical supervision. Your body needs at least this much energy for basic functions. Sustained intake below BMR can trigger metabolic adaptation, muscle loss, and hormonal disruptions. Aim for a calorie target between your BMR and TDEE.

How This Is Calculated

Male BMR (kcal) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 Female BMR (kcal) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161 BMR (kJ) = BMR (kcal) × 4.184

weight: = Body weight in kilograms
height: = Height in centimetres
age: = Age in years
4.184: = Conversion factor from kcal to kJ

The Mifflin-St Jeor equation (1990) is the primary formula used. The Harris-Benedict revised equation (1984) is shown for comparison. Both are validated for healthy adults aged 18-65.

Related Tools

TDEE Calculator

Calculate your Total Daily Energy Expenditure using the Mifflin-St Jeor equation. See how many calories and kilojoules you burn per day.

Calorie Deficit Calculator

Calculate your optimal calorie deficit for weight loss. See how long it will take to reach your goal weight with a safe, sustainable deficit.

Metabolic Age Calculator

Calculate your metabolic age by comparing your BMR to average values for different age groups.

Disclaimer

This calculator provides estimates for informational purposes only and should not be considered medical advice. Individual results may vary based on factors not captured by these formulas. Consult a healthcare professional before making changes to your diet or exercise routine, especially if you have any existing health conditions.