How Many Calories Should I Eat a Day?
Calorie intake calculator
The Harris-Benedict equation, also known as the Harris-Benedict principle, is used to estimate what a person's BMR (basal metabolic rate) and daily requirements are.
Your BMR total is multiplied by another number which represents your level of physical activity. The resulting number is your recommended daily calorie intake in order to keep your body weight where it is.
This equation has some limitations. It does not take into account varying levels of muscle mass to fat mass ratios - a very muscular person needs more calories, even when resting.
- Male adults
66.5 + (13.75 x kg body weight) + (5.003 x height in cm) - (6.755 x age) = BMR
66 + ( 6.23 x pounds body weight) + ( 12.7 x height in inches ) - ( 6.76 x age) = BMR
- Female adults
55.1 + (9.563 x kg body weight) + (1.850 x height in cm) - (4.676 x age) = BMR
655 + (4.35 x kg body weight) + (4.7 x height in inches) - (4.7 x age) = BMR
Daily calorie calculators
You can use our BMR calculators below to work out your BMR and daily calorie recommendation. One calculator uses metric measurements and the other uses imperial measurements - the choice is yours.
our daily calorie requirement
To work out a figure for your daily calorie requirement, we apply levels of physical activity to the equation as per the guide below. If you have entered information into the calculator above, you'll see your personal calculations:
- Sedentary lifestyle - if you do very little or no exercise at all
Your daily calorie requirement is BMR x 1.2.
- Slightly active lifestyle - light exercise between once and three times per week
Your daily calorie requirement is BMR x 1.375.
- Moderately active lifestyle - if you do moderate exercise three to five days per week
Your daily calorie requirement is BMR x 1.55.
- Active lifestyle - if you do intensive/heavy exercise six to seven times per week
Your daily calorie requirement is BMR x 1.725.
- Very active lifestyle - if you do very heavy/intensive exercise twice a day (extra heavy workouts
Your daily calorie requirement is BMR x 1.9.
The human body and energy usage
For the human body to remain alive, it requires energy. Approximately 20% of the energy we use is for brain metabolism. The majority of the rest of the body's energy requirements are taken up for the basal metabolic requirements - the energy we need when in a resting state, for functions such as the circulation of the blood and breathing.
If our environment is cold, our metabolism increases to produce more heat to maintain a constant body temperature. When we are in a warm environment, we require less energy.
We also require mechanical energy for our skeletal muscles for posture and moving around.
Respiration, or specifically cellular respiration refers to the metabolic process by which an organism gets energy by reacting oxygen with glucose to produce carbon dioxide, water and ATP energy. How efficiently energy from respiration converts into physical (mechanical) power depends on the type of food eaten, as well as what type of physical energy is used - whether muscles are used aerobically or anaerobically.
Put simply - we need calories to stay alive, even if we are not moving, and need calories to keep our posture and to move about.