BMI & BMR Calculator
Calculate both BMI and Basal Metabolic Rate.
Step-by-Step Solution
About BMI & BMR Calculator
Calculate both BMI and Basal Metabolic Rate. This calculator provides instant results with step-by-step explanations to help you understand the calculation process.
How to use this calculator
- Enter your weight, height, age, and sex into the calculator.
- Choose the units that match your measurements.
- Run the calculation to get both BMI and BMR instantly.
- Use the step-by-step breakdown to see how each result was computed.
The formula explained
$$ \text{BMI} = \frac{\text{weight}}{\text{height}^2} \quad \text{and} \quad \text{BMR}_{\text{men}} = 10w + 6.25h - 5a + 5 \quad \text{or} \quad \text{BMR}_{\text{women}} = 10w + 6.25h - 5a - 161 $$
- \(\text{BMI}\) = body mass index
- \(\text{weight}\) = body weight in kilograms
- \(\text{height}\) = height in meters for BMI, and in centimeters for BMR
- \(\text{BMR}\) = basal metabolic rate
- \(w\) = weight in kilograms
- \(h\) = height in centimeters
- \(a\) = age in years
- \(\text{men}\) = male BMR formula
- \(\text{women}\) = female BMR formula
Step by step method
- First, the calculator converts your inputs into the units needed for each formula.
- Next, it computes BMI by dividing weight by height squared.
- Then, it computes BMR using the appropriate sex-based equation.
- Finally, it shows the results and the working so you can check the calculation.
Worked example
For example, suppose a 30-year-old woman weighs 68 kilograms and is 170 centimeters tall.
- Compute BMI using height in meters: \(170 \text{ cm} = 1.70 \text{ m}\), so \(\text{BMI} = 68 \div (1.70 \times 1.70)\).
- That gives \(\text{BMI} = 68 \div 2.89 \approx 23.53\).
- Compute BMR for a woman: \(10(68) + 6.25(170) - 5(30) - 161 = 680 + 1062.5 - 150 - 161\).
- So the BMR is \(1431.5\) calories per day.
Answer. BMI is about 23.53, and BMR is 1431.5 calories per day.
Tips and common mistakes
- Use kilograms and centimeters for the BMR formula, and meters for BMI height if the calculator does not convert automatically.
- Do not square the height in centimeters when calculating BMI unless the tool explicitly tells you to convert first.
- Choose the correct sex option for BMR, since the formula changes by sex.
- BMI is a screening measure, not a full health diagnosis, so interpret it with context.
Frequently asked questions
What is BMI used for?+
BMI is a quick screening measure that compares weight to height. It can help estimate whether someone is in a lower, healthier, or higher weight range. It does not tell you everything about body composition or health.
What is BMR?+
BMR is the number of calories your body uses at rest to keep basic functions going. It is a starting point for understanding daily energy needs. Activity level is not included in BMR.
Why do I need to choose sex?+
The BMR formula used by this tool depends on sex because the standard equation changes. Choosing the correct option helps the calculator return the right result. BMI does not depend on sex, but BMR does in this calculator.
Can I use pounds and inches?+
Some calculators convert units automatically, but the formulas here require specific units. If the tool accepts imperial units, it will convert them for you before calculating. If not, convert to kilograms and centimeters first.
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