Ideal Body Weight: What the Formulas Mean and Which One to Use
“What should I weigh for my height?” is one of the most common health questions — and it does not have a single perfect answer. Multiple clinical formulas exist, each developed for different purposes, and they often give slightly different numbers. This guide explains what each formula means, how to calculate your ideal body weight, and which metric actually matters most for your health.
Use our Ideal Weight Calculator to get your result from all major formulas simultaneously.
Why There Are Multiple Ideal Weight Formulas
Ideal Body Weight (IBW) formulas were originally designed not for fitness, but for clinical medicine — specifically to calculate drug dosages that depend on patient size. The four most common formulas were each developed by different researchers between the 1960s and 1980s:
| Formula | Year | Developed For |
|---|---|---|
| Devine | 1974 | Adjusting gentamicin doses |
| Robinson | 1983 | Revised clinical dosing |
| Miller | 1983 | Alternative clinical dosing |
| Hamwi | 1964 | Diabetes patient counseling |
None of these were originally meant to tell you what you should weigh for optimal health. Over time, they became widely used as health benchmarks because they provide a simple, height-based target.
The Four Major Ideal Weight Formulas
1. Devine Formula (Most Commonly Used)
Men: IBW = 50 kg + 2.3 kg for every inch over 5 feet (152.4 cm) Women: IBW = 45.5 kg + 2.3 kg for every inch over 5 feet
Example: A 5’8” (172.7 cm) man: Inches over 5 feet = 8 inches IBW = 50 + (2.3 × 8) = 50 + 18.4 = 68.4 kg
2. Robinson Formula
Men: IBW = 52 kg + 1.9 kg for every inch over 5 feet Women: IBW = 49 kg + 1.7 kg for every inch over 5 feet
Same 5’8” man: IBW = 52 + (1.9 × 8) = 52 + 15.2 = 67.2 kg
3. Miller Formula
Men: IBW = 56.2 kg + 1.41 kg for every inch over 5 feet Women: IBW = 53.1 kg + 1.36 kg for every inch over 5 feet
Same 5’8” man: IBW = 56.2 + (1.41 × 8) = 56.2 + 11.28 = 67.5 kg
4. Hamwi Formula
Men: IBW = 48 kg + 2.7 kg for every inch over 5 feet Women: IBW = 45.5 kg + 2.2 kg for every inch over 5 feet
Same 5’8” man: IBW = 48 + (2.7 × 8) = 48 + 21.6 = 69.6 kg
As you can see, all four formulas give similar but distinct results. The Devine formula is the most commonly cited.
Converting to Metric (For Heights in cm)
If your height is in centimetres:
- Subtract 152.4 cm from your height
- Divide by 2.54 to get inches over 5 feet
- Apply the formula
Example: 175 cm tall man using Devine: (175 − 152.4) = 22.6 cm above 5 feet 22.6 ÷ 2.54 = 8.9 inches over 5 feet IBW = 50 + (2.3 × 8.9) = 50 + 20.47 = 70.5 kg
What is a Healthy Weight Range?
The IBW formulas give a single target number. In practice, a healthy weight range is more useful. This is typically defined as:
Healthy Range = IBW ± 10%
For a 70 kg IBW:
- Lower bound: 70 × 0.90 = 63 kg
- Upper bound: 70 × 1.10 = 77 kg
Most healthcare providers consider anyone within ±10% of their IBW to be at a healthy weight.
Ideal Weight vs. BMI: Which is Better?
Both IBW and BMI are height-based weight standards, but they work differently:
| Metric | Measures | Limitation |
|---|---|---|
| BMI | Weight relative to height (kg/m²) | Does not account for gender or body frame |
| IBW | Target weight based on height and gender | Uses a single target number, ignores muscle mass |
BMI gives you a category (underweight/normal/overweight/obese). IBW gives you a specific target weight. Neither accounts for body fat percentage, which is the most accurate health indicator.
Use our BMI Calculator alongside the Ideal Weight Calculator for a more complete picture.
Ideal Weight for Women vs. Men
Women naturally carry a higher proportion of essential body fat than men. This is why all IBW formulas have separate equations for men and women — women’s ideal weights are set lower for the same height, reflecting healthy physiological differences.
Example: 5’6” (167.6 cm) tall person:
- Man (Devine): 50 + (2.3 × 6) = 63.8 kg
- Woman (Devine): 45.5 + (2.3 × 6) = 59.3 kg
A 4.5 kg difference for the same height, purely based on gender.
Limitations of Ideal Body Weight
Athletes and Muscular Individuals
Muscle weighs more than fat. An athlete with very low body fat may weigh significantly above their IBW while being in peak health. IBW formulas treat a bodybuilder and an office worker with the same height identically — which is clinically inappropriate.
Elderly Individuals
As people age, they naturally lose muscle mass (sarcopenia) and bone density. An elderly person at their “ideal weight” might actually be at an unhealthy body composition. Some geriatric guidelines suggest a slightly higher target weight for older adults.
Frame Size Variation
Body frame size (small, medium, large) significantly affects what a healthy weight looks like. Some formulas attempt to adjust for wrist circumference as a proxy for frame size. The IBW range (±10%) partially accommodates this.
Children and Adolescents
All four IBW formulas are designed for adults only. For children, BMI-for-age percentile charts (specific to age and gender) are the appropriate measure.
How to Use Ideal Weight as a Goal
If you want to reach your ideal weight:
- Calculate the gap: Current weight − IBW = kg to lose (or gain)
- Set a realistic timeline: Safe weight loss is 0.5–1 kg per week
- Calculate the required calorie deficit: ~7,700 calories ≈ 1 kg of body fat
- Track with tools: Use our Calorie Calculator to find your TDEE, then create a deficit
Example: Current weight 85 kg, IBW 70 kg → 15 kg to lose At 0.5 kg/week: 15 ÷ 0.5 = 30 weeks (about 7 months) At 0.75 kg/week: 15 ÷ 0.75 = 20 weeks (about 5 months)
For all these calculations, start with our Ideal Weight Calculator to determine your target, then use the Calorie Calculator to plan your nutritional strategy.