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Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in meters squared. For those using the imperial system, the formula is BMI = 703 × lb/in² where lb is the weight in pounds and in² is the height in inches squared.
Metric Formula:
Imperial Formula:
For a person who is 175 cm tall and weighs 70 kg:
175 cm ÷ 100 = 1.75 m
1.75 m × 1.75 m = 3.0625 m²
70 kg ÷ 3.0625 m² = 22.86 kg/m²
Classification: Normal weight
For a person who is 5'9" (69 inches) tall and weighs 160 pounds:
69 in × 69 in = 4,761 in²
160 lb × 703 = 112,480
112,480 ÷ 4,761 = 23.63
Classification: Normal weight
While BMI is a useful tool for assessing weight status for most people, it does have some important limitations:
A muscular athlete might have a high BMI despite having low body fat
Two people with the same BMI can have different amounts of body fat
Different populations may have different healthy BMI ranges
Different assessment methods should be used for these groups
While the standard BMI categories apply to most adults aged 20 and over, there are some age-related considerations:
Age Group | BMI Considerations |
|---|---|
| Children and teens (2-19) | Use age and gender-specific percentiles instead of the standard BMI categories |
| Adults (20-65) | Standard BMI categories apply |
| Older adults (65+) | Some research suggests a slightly higher BMI (23-30) may be beneficial |
Research has shown that different ethnic groups may have different associations between BMI, percentage of body fat, and health risks. For example:
May have health risks at lower BMIs than Europeans. Some Asian countries define overweight as a BMI ≥ 23
May have lower body fat and higher lean muscle mass at the same BMI compared to white populations
Regardless of your current BMI, here are evidence-based strategies for maintaining a healthy weight:
Emphasize fruits, vegetables, whole grains, lean proteins, and healthy fats
Use smaller plates and be mindful of serving sizes
Drink water before meals and limit sugary beverages
Prepare healthy meals and snacks to avoid impulsive, unhealthy choices
Pay attention to hunger and fullness cues, eat slowly
Or 75 minutes of vigorous activity, plus strength training twice a week
You're more likely to stick with exercise you find pleasurable
Short bursts of activity throughout the day add up
Stand or move around for a few minutes every hour
Building muscle helps maintain a healthy metabolism
Aim for 7-9 hours of quality sleep per night; poor sleep is linked to weight gain
Chronic stress can lead to emotional eating and weight gain; try meditation, yoga, or other stress-reduction techniques
Regularly monitor your weight, BMI, and other health metrics to stay accountable
Consult with healthcare providers for personalized advice and support
Due to the limitations of BMI, consider using these additional measurements:
Measures abdominal fat; for reduced health risk: men < 40 inches (102 cm), women < 35 inches (88 cm)
Waist measurement divided by hip measurement; ideal: men < 0.9, women < 0.85
Directly measures proportion of fat in body; healthy ranges vary by age and gender
Watch this short video to learn more about BMI, how it's calculated, and what the different categories mean for your health.