What Does "Ideal Weight" Actually Mean?
The concept of an "ideal weight" has been around for over a century, but its meaning has evolved significantly. Originally, ideal weight tables were created by insurance companies in the early 1900s to assess mortality risk. Today, we understand that ideal weight isn't a single magic number — it's a range that accounts for individual differences in body composition, frame size, age, sex, and muscle mass.
The term is somewhat misleading because it implies a universal standard. In reality, two people of the same height can have very different healthy weights depending on their body composition. A powerlifter and a marathon runner of the same height might have a 30-40 pound difference in weight, yet both could be in excellent health. What matters most is your body fat percentage, not your weight alone.
That said, ideal weight formulas still serve a useful purpose: they provide a reasonable starting point and a frame of reference for setting health goals. Our ideal weight calculator compares results from multiple formulas to give you a comprehensive picture.
The Major Ideal Weight Formulas
Over the past century, several researchers have developed formulas to estimate ideal body weight. Each uses height as the primary input and was derived from different study populations. Understanding the differences helps you interpret results intelligently.
The Devine Formula (1974)
Dr. B.J. Devine developed this formula for calculating ideal body weight for medicinal dosage purposes. It became the most widely used formula in clinical settings for decades and remains common today.
Men: IBW = 50 kg + 2.3 kg per inch over 5 feet Women: IBW = 45.5 kg + 2.3 kg per inch over 5 feet
For a 5'10" (70 inch) man: 50 + (10 × 2.3) = 73 kg (160.9 lbs). For a 5'5" (65 inch) woman: 45.5 + (5 × 2.3) = 57 kg (125.7 lbs).
Criticism: The Devine formula tends to underestimate ideal weight for taller individuals and doesn't account for frame size or age. It was originally based on a limited sample and may not represent modern populations well.
The Robinson Formula (1983)
Dr. J.D. Robinson modified the Devine formula after observing that Devine's estimates for women were too low. His adjustments produced slightly higher values for women while keeping men's values similar.
Men: IBW = 52 kg + 1.9 kg per inch over 5 feet Women: IBW = 49 kg + 1.7 kg per inch over 5 feet
The Robinson formula generally produces results that align more closely with modern BMI-based healthy ranges, particularly for women.
The Miller Formula (1983)
Dr. D.R. Miller proposed this formula as an alternative that was less influenced by the original Metropolitan Life Insurance tables, which many researchers considered biased toward smaller body sizes.
Men: IBW = 56.2 kg + 1.41 kg per inch over 5 feet Women: IBW = 53.1 kg + 1.36 kg per inch over 5 feet
The Miller formula tends to give slightly higher ideal weights than Devine and Robinson, particularly for shorter individuals.
The Hamwi Formula (1964)
Dr. G.J. Hamwi developed this formula for clinical use in calculating drug dosages. It's still commonly used in pharmacy and clinical nutrition settings.
Men: IBW = 48 kg + 2.7 kg per inch over 5 feet Women: IBW = 45.5 kg + 2.2 kg per inch over 5 feet
The Hamwi formula allows for frame size adjustments: add 10% for a large frame, subtract 10% for a small frame. This makes it one of the few formulas that explicitly accounts for body frame differences.
Comparing the Formulas
Here's how the formulas compare for a 5'10" man and a 5'5" woman:
| Formula | Men (5'10") | Women (5'5") |
|---|---|---|
| Devine | 73.0 kg (160.9 lbs) | 57.0 kg (125.7 lbs) |
| Robinson | 70.9 kg (156.3 lbs) | 57.5 kg (126.8 lbs) |
| Miller | 68.0 kg (149.9 lbs) | 57.9 kg (127.6 lbs) |
| Hamwi | 75.0 kg (165.3 lbs) | 56.5 kg (124.6 lbs) |
Notice the variation — the same person gets different ideal weights depending on which formula is used. This is why the best approach is to look at all formulas together and consider the range they produce, rather than fixating on any single number.
Body Frame Size: The Missing Variable
Most ideal weight formulas don't account for body frame size, which can cause significant error. A person with a large frame naturally carries more bone and muscle mass than a small-framed person of the same height, and their healthy weight will be correspondingly higher.
How to Determine Your Frame Size
The simplest method is the wrist circumference test:
- Women: Height under 5'2" — wrist under 5.5" is small, 5.5-5.75" is medium, over 5.75" is large. Height 5'2"-5'5" — wrist under 6" is small, 6-6.25" is medium, over 6.25" is large. Height over 5'5" — wrist under 6.25" is small, 6.25-6.5" is medium, over 6.5" is large.
- Men: Height over 5'5" — wrist under 6.5" is small, 6.5-7.5" is medium, over 7.5" is large.
A quick alternative: wrap your thumb and middle finger around the wrist just above the bone. If fingers overlap, small frame. If they just touch, medium frame. If there's a gap, large frame.
Frame Size Adjustments
For the Hamwi formula, add or subtract 10% based on frame size. For other formulas, a general rule of thumb is to adjust by 5-10%:
- Small frame: Subtract 5-10% from the calculated ideal weight
- Medium frame: Use the calculated ideal weight as-is
- Large frame: Add 5-10% to the calculated ideal weight
For a large-framed 5'10" man with a Hamwi ideal weight of 165 lbs, the adjusted range would be 165-182 lbs. That's a meaningful difference of 17 pounds.
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Try the Ideal Weight Calculator →Why BMI and Ideal Weight Don't Tell the Whole Story
BMI (Body Mass Index) is the most commonly used screening tool for weight-related health, but it has significant limitations. BMI uses only height and weight and cannot distinguish between fat mass and lean mass. This creates two major problems:
- Falsely classifying muscular people as overweight: A 5'10" man at 200 lbs who is 12% body fat has a BMI of 28.7 — technically "overweight" — despite being in excellent shape.
- Falsely classifying thin people as healthy: A 5'5" woman at 125 lbs who is 32% body fat has a "normal" BMI of 20.8, but her body composition indicates elevated health risk.
This is why ideal weight should always be considered alongside body fat percentage and other health markers like waist circumference, blood pressure, blood sugar, and lipid panels. A number on a scale or a formula result is just one data point in a much larger picture.
Age and Ideal Weight
Ideal weight is not static throughout life. As we age, several factors change the relationship between weight and health:
- Muscle loss (sarcopenia): Adults lose 3-8% of muscle mass per decade after age 30. Since muscle weighs more than fat by volume, this natural decline means older adults may weigh less even if their fat mass increases.
- Bone density changes: Bone density decreases with age, particularly after menopause in women, contributing to a gradual decrease in total weight.
- Metabolic changes: Basal metabolic rate declines with age, making it easier to gain fat and harder to lose it.
- The "obesity paradox": Research consistently shows that a slightly higher BMI (23-27) in adults over 65 is associated with lower mortality than lower BMIs. This suggests that the ideal weight range shifts upward with age.
For adults over 65, many geriatricians recommend aiming for a BMI of 23-27 rather than the standard 18.5-24.9 range. The extra weight reserve can protect against frailty, immune suppression, and delayed recovery from illness.
Setting Realistic Weight Goals
If you're trying to reach your ideal weight, here are some evidence-based principles for setting realistic, sustainable goals:
- Use the range, not a single number. If formulas give you a range of 140-160 lbs, your target is the entire range — not the lowest number.
- Focus on body composition, not just weight. Building muscle through strength training will increase your weight while improving your health. Track body fat percentage alongside scale weight.
- Set process goals, not outcome goals. Instead of "lose 20 pounds," aim for "exercise 4 times per week and eat vegetables with every meal." Process goals are within your control; outcome goals are not.
- Aim for 0.5-1% of body weight per week. Faster weight loss almost always means more muscle loss and a higher likelihood of regaining the weight.
- Recalculate after significant weight changes. Your TDEE decreases as you lose weight. What worked at 200 lbs won't work at 170 lbs.
Frequently Asked Questions
How do I know my body frame size?
Wrap your thumb and middle finger around your wrist just above the wrist bone. If your fingers overlap, you have a small frame. If they just touch, you have a medium frame. If there's a gap, you have a large frame.
Is ideal weight the same as healthy weight?
Not exactly. "Ideal weight" refers to a specific target from a formula, while "healthy weight" is a broader range based on BMI (18.5-24.9). Your ideal weight might fall within the healthy range, but the range itself allows for individual variation.
Why do different ideal weight formulas give different results?
Each formula was developed by different researchers using different study populations and methodologies. The Devine formula (1974) was based on ideal body weights for medicinal dosage calculations. The Miller formula (1983) was based on average weights of insured people. These differences lead to slightly different estimates.
Can muscle mass make me weigh more than my ideal weight?
Yes, absolutely. Muscle is denser than fat, so a muscular person can weigh significantly more than their ideal weight while having excellent health and low body fat. This is a major limitation of ideal weight formulas.
Does age affect ideal weight?
Yes. Research shows that a BMI of 23-27 for adults over 65 is associated with lower mortality than a BMI of 18.5-22. Older adults tend to lose muscle mass, so maintaining a slightly higher weight becomes more important for health.
Key Takeaways
- Ideal weight is a range, not a single number — different formulas give different results, and that's okay.
- Body frame size significantly affects your ideal weight. Adjust by 5-10% for small or large frames.
- Body composition matters more than weight — a muscular person can be healthy well above their calculated ideal weight.
- Age shifts the ideal weight range upward, especially after 65, where slightly higher weight is protective.
- Use ideal weight as a general reference point, not an absolute target. Focus on sustainable habits and overall health markers.