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BMR Calculator - Mifflin-St Jeor, Harris-Benedict, Revised Harris-Benedict, Katch-McArdle, Schofield Formula

BMR Calculator

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1. What is a BMR Calculator?

Definition: This calculator computes your Basal Metabolic Rate (BMR) using five different methods, estimating the calories your body needs at rest to maintain basic functions.

Purpose: It helps determine your daily calorie needs for nutritional planning, weight management, or fitness goals, providing a comparison across multiple methods for better insight.

2. How Does the Calculator Work?

The calculator takes sex, age, height, weight, and optionally body fat percentage with selectable units, and computes BMR using all five methods:

  • Mifflin-St Jeor:
    • Men: \( \text{BMR} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age} + 5 \).
    • Women: \( \text{BMR} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age} - 161 \).
  • Harris-Benedict (Original):
    • Men: \( \text{BMR} = 66.5 + 13.75 \times \text{weight (kg)} + 5.003 \times \text{height (cm)} - 6.755 \times \text{age} \).
    • Women: \( \text{BMR} = 655.1 + 9.563 \times \text{weight (kg)} + 1.850 \times \text{height (cm)} - 4.676 \times \text{age} \).
  • Revised Harris-Benedict:
    • Men: \( \text{BMR} = 88.362 + 13.397 \times \text{weight (kg)} + 4.799 \times \text{height (cm)} - 5.677 \times \text{age} \).
    • Women: \( \text{BMR} = 447.593 + 9.247 \times \text{weight (kg)} + 3.098 \times \text{height (cm)} - 4.330 \times \text{age} \).
  • Katch-McArdle:
    • LBM (if body fat provided): \( \text{LBM} = (\text{weight (kg)} \times (1 - \text{Body Fat \%})) / 100 \).
    • LBM (Boer formula, men): \( \text{LBM} = 0.407 \times \text{weight (kg)} + 0.267 \times \text{height (cm)} - 19.2 \).
    • LBM (Boer formula, women): \( \text{LBM} = 0.252 \times \text{weight (kg)} + 0.473 \times \text{height (cm)} - 48.3 \).
    • BMR: \( \text{BMR} = 370 + (21.6 \times \text{LBM (kg)}) \).
  • Schofield:
    • Men (≤30 years): \( \text{BMR} = 15.057 \times \text{weight (kg)} + 692.2 \).
    • Men (>30 years): \( \text{BMR} = 11.472 \times \text{weight (kg)} + 873.1 \).
    • Women (≤30 years): \( \text{BMR} = 14.818 \times \text{weight (kg)} + 486.6 \).
    • Women (>30 years): \( \text{BMR} = 8.126 \times \text{weight (kg)} + 845.6 \).

Unit Conversions:

  • Height: cm, m, in, ft (e.g., 1 m = 100 cm = 39.3701 in).
  • Weight: kg, lb, oz (e.g., 1 kg = 2.20462 lb).

Steps:

  • Select your sex.
  • Input your age, height, and weight with chosen units.
  • For Katch-McArdle, choose to input body fat percentage or estimate LBM.
  • Compute your BMR using all methods.

3. Importance of BMR Calculations

Calculating BMR is useful for:

  • Nutritional Planning: Determines the baseline calories needed at rest, which can be adjusted for activity to plan diets.
  • Weight Management: Helps set calorie goals for maintaining, gaining, or losing weight, with multiple methods providing a range of estimates.
  • Personalized Health: Offers a comparison across methods to find the most suitable estimate for your body composition and lifestyle.

4. Using the Calculator

Examples:

  • Male, Age 30: Height = 180 cm, Weight = 70 kg
    Mifflin-St Jeor: \( 10 \times 70 + 6.25 \times 180 - 5 \times 30 + 5 \approx 1480.00 \, \text{kcal/day} \).
    Harris-Benedict (Original): \( 66.5 + 13.75 \times 70 + 5.003 \times 180 - 6.755 \times 30 \approx 1726.04 \, \text{kcal/day} \).
    Revised Harris-Benedict: \( 88.362 + 13.397 \times 70 + 4.799 \times 180 - 5.677 \times 30 \approx 1715.88 \, \text{kcal/day} \).
    Katch-McArdle (Boer LBM = 61.21 kg): \( 370 + 21.6 \times 61.21 \approx 1692.14 \, \text{kcal/day} \).
    Schofield (>30 years): \( 11.472 \times 70 + 873.1 \approx 1676.14 \, \text{kcal/day} \).
  • Female, Age 25: Height = 165.1 cm, Weight = 60 kg, Body Fat = 25% (for Katch-McArdle)
    Mifflin-St Jeor: \( 10 \times 60 + 6.25 \times 165.1 - 5 \times 25 - 161 \approx 1346.88 \, \text{kcal/day} \).
    Harris-Benedict (Original): \( 655.1 + 9.563 \times 60 + 1.850 \times 165.1 - 4.676 \times 25 \approx 1407.64 \, \text{kcal/day} \).
    Revised Harris-Benedict: \( 447.593 + 9.247 \times 60 + 3.098 \times 165.1 - 4.330 \times 25 \approx 1406.01 \, \text{kcal/day} \).
    Katch-McArdle (LBM = 45.00 kg): \( 370 + 21.6 \times 45.00 \approx 1342.00 \, \text{kcal/day} \).
    Schofield (≤30 years): \( 14.818 \times 60 + 486.6 \approx 1375.68 \, \text{kcal/day} \).

5. Frequently Asked Questions (FAQ)

Q: What does BMR represent?
A: BMR represents the number of calories your body needs at rest to maintain basic functions like breathing, circulation, and cell production, measured in kcal/day.

Q: Why calculate BMR with multiple methods?
A: Different methods account for varying factors and populations, providing a range of estimates. For example, Mifflin-St Jeor is often more accurate for modern populations, Katch-McArdle is better for those with known body fat percentages, and Schofield simplifies the calculation by focusing on weight.

Q: How do I interpret the different BMR results?
A: Compare the results to understand the range of your possible BMR. If you know your body fat percentage, Katch-McArdle may be more accurate. For a general estimate, Mifflin-St Jeor is often recommended. Use the range to inform your calorie needs, consulting a professional for personalized advice.

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