Ideal Weight Calculator: Compare Robinson, Miller, Devine & Hamwi Formulas
Calculate your ideal weight using four historical medical formulas (Robinson, Miller, Devine, Hamwi) plus healthy BMI range. Get personalized results adjusted for frame size, gender, and height with educational information about formula origins and differences.
What This Calculator Does & Who It's For
Calculator Purpose & Outputs
- What You'll Get:
Average Ideal Weight: The mean of all four formulas, giving you a balanced estimate. When frame size is selected, this shows the frame-adjusted average (midpoint of the adjusted range).
Formula Comparison Table: Side-by-side results from Robinson (1983), Miller (1983), Devine (1974), and Hamwi (1964) formulas. Each shows its original purpose—Robinson for medical dosing, Miller from clinical studies, Devine for drug clearance, Hamwi for general wellness.
Frame Size Adjusted Ranges: When you select your frame size, each formula displays a range (±10% adjustment) instead of a single number. Small frame: -10% to -5%. Large frame: +5% to +10%. This accounts for natural bone structure differences.
Healthy BMI Range: The weight range corresponding to BMI 18.5-25, displayed alongside formula results so you can see how ideal weight formulas compare to modern health standards.
Frame Size Guide: Interactive modal with step-by-step wrist measurement instructions and gender-specific frame size ranges.
(Note: This calculator is for educational purposes only and does not provide medical advice.)
- Calculation Methods:
Robinson Formula (1983):
Men: Ideal Weight = 52 kg + 1.9 kg × (inches over 5 feet)Originally developed for medical drug dosing calculations.
Women: Ideal Weight = 49 kg + 1.7 kg × (inches over 5 feet)Miller Formula (1983):
Men: Ideal Weight = 56.2 kg + 1.41 kg × (inches over 5 feet)Based on clinical study data.
Women: Ideal Weight = 53.1 kg + 1.36 kg × (inches over 5 feet)Devine Formula (1974):
Men: Ideal Weight = 50 kg + 2.3 kg × (inches over 5 feet)Created for drug clearance calculations.
Women: Ideal Weight = 45.5 kg + 2.3 kg × (inches over 5 feet)Hamwi Formula (1964):
Men: Ideal Weight = 48 kg + 2.7 kg × (inches over 5 feet)Developed for general wellness assessment.
Women: Ideal Weight = 45.5 kg + 2.2 kg × (inches over 5 feet)Frame Size Adjustment: Small frame: -10% to -5%, Medium: -3% to +3%, Large: +5% to +10% applied to all formula results.
Healthy BMI Range: Calculated as BMI 18.5-25 based on height:
Weight = BMI × (Height (m))² - Ideal Users:
Individuals seeking ideal weight guidance: Want to see how different historical formulas calculate ideal weight? Compare Robinson vs. Devine vs. Hamwi results side-by-side. Get the average across all methods, plus frame size adjustments that personalize the results.
Weight management: Need multiple perspectives on your target weight? These formulas give you four different angles—from conservative medical dosing (Robinson) to general wellness (Hamwi). Frame size adjustments create personalized ranges so you're not chasing a single number.
Health-conscious individuals: Curious about why ideal weight formulas exist? Learn their origins (hint: most were for drug dosing, not aesthetics). Understand how they relate to the healthy BMI range. Discover why frame size matters more than most people realize.
Healthcare providers: Looking for an educational tool for patient discussions? This calculator helps explain why ideal weight isn't one number, how formulas differ, and when body composition matters more than total weight.
Fitness enthusiasts: Athletes and bodybuilders often "fail" ideal weight formulas because they don't account for muscle mass. This tool helps explain why, and when to use body fat percentage instead.
(Note: This calculator is for educational purposes only and does not provide medical advice, diagnosis, or treatment.)
- Accuracy & Limitations:
Ideal weight formulas are estimates based on population averages, and they have some important limitations:
Muscle mass blind spot: These formulas can't tell the difference between muscle and fat. A bodybuilder at 180 lbs might be healthier than a sedentary person at 160 lbs, but the formulas don't know that. If you're highly active or muscular, body fat percentage is more useful than ideal weight.
Age isn't factored in: Formulas don't account for age-related muscle loss (sarcopenia). A 70-year-old at "ideal weight" might have 30% body fat, while a 30-year-old at the same weight has 20% body fat. As you age, body composition matters more than total weight.
Body composition varies: Two people can have the same ideal weight but completely different body compositions. One might be 15% body fat (athletic), the other 25% body fat (sedentary). The formulas can't distinguish between them.
Formula variation is normal: The 5-15 lb difference between formulas isn't error—it's evidence that "ideal" weight is inherently a range. Robinson (lowest) prioritizes medical safety. Hamwi (highest) emphasizes wellness. The variation reflects their different purposes.
Medical origins: Most formulas were created for drug dosing calculations, not aesthetic goals or general health. They're conservative by design, prioritizing safety over appearance.
Important: This calculator is for educational and informational purposes only. It does not provide medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for personalized weight management guidance, especially if you have underlying health conditions, are pregnant, or are considering significant weight changes.
Understanding Ideal Weight Formulas: Origins & Differences
The Origin of "Ideal" Weight Formulas
- Robinson Formula (1983) - Medical Dosage:Dr. J.D. Robinson created this formula specifically for calculating medication dosages. When doctors need to prescribe drugs based on body weight, they need conservative estimates—better to under-dose slightly than risk overdose. That's why Robinson uses lower coefficients, resulting in lower ideal weights. It's still widely used in hospitals and clinics today because safety margins matter more than precision when it comes to medications. If Robinson gives you a lower number than expected, remember: it's designed to be cautious.
- Miller Formula (1983) - Clinical Study:Unlike Robinson and Devine (which were built for drug calculations), Miller came from analyzing actual health outcomes in clinical studies. Researchers looked at large datasets to find what weights correlated with better health. The result? A middle-ground formula that's more balanced than Robinson (which is ultra-conservative) but less liberal than Hamwi. Miller tends to produce results that fall right in the middle of the formula spread, making it a solid "average" estimate for general health assessment.
- Devine Formula (1974) - Drug Clearance:Dr. B.J. Devine developed this for a different medical problem: drug clearance rates. When your body processes medications, it needs enough metabolic capacity to clear them efficiently. That requires different weight estimates than dosing calculations. Devine uses higher coefficients than Robinson, resulting in higher ideal weights. The logic? If you're calculating how fast someone's body can process a drug, you need to account for metabolic function, which correlates with body composition. Devine is still used in pharmacokinetic research today.
- Hamwi Formula (1964) - General Wellness:Here's the outlier: Hamwi is the only formula originally created for general wellness, not medical dosing. Dr. G.J. Hamwi developed it in 1964 to help people assess their health, not calculate drug dosages. That's why it uses the highest coefficients, resulting in the highest ideal weights. Hamwi emphasizes metabolic health and achievable wellness goals rather than ultra-conservative safety margins. If you find Hamwi's numbers more realistic or achievable, that's probably why—it was designed with general health in mind, not medical safety.
- Why Formulas Differ (And Why That's Okay):The 5-15 lb variation between formulas isn't a bug—it's a feature. Each formula was built for a different purpose: Robinson prioritizes medical safety (lower weights = safer dosing). Devine accounts for metabolic function (higher weights = better clearance estimates). Miller balances multiple health factors (middle ground). Hamwi emphasizes achievable wellness (higher weights = more realistic goals). This variation actually tells you something important: "ideal" weight is inherently subjective and context-dependent. There's no single "right" answer. The average of all four formulas often provides the most balanced estimate because it accounts for these different perspectives. When you see this spread, don't stress about which formula is "correct." Instead, recognize that your ideal weight exists somewhere in that range, adjusted for your individual frame size and body composition.
Body Frame Size: Measurement & Adjustment
How to Measure and Use Frame Size
- How to Measure Wrist Circumference (The Right Way):
Measuring your wrist sounds simple, but there's a trick to getting it right.
Step 1: Find the narrowest point of your wrist—it's usually just below the wrist bone, right where your hand meets your arm. This is important because measuring at the wrong spot can throw off your frame size classification.
Step 2: Wrap a flexible measuring tape (or a piece of string) around this narrowest point.
Step 3: Make it snug but not tight. You want it to sit comfortably without compressing your skin. If it leaves a mark, it's too tight.
Step 4: Read the measurement in inches.
Step 5: Compare to the ranges below based on your biological sex.
Pro tip: If you don't have a measuring tape, use a piece of string, mark where it overlaps, then measure the string against a ruler. Measure your dominant hand's wrist for consistency—most people have slightly different wrist sizes on each side.
- Frame Size Ranges by Gender:
Men: Small frame: < 6.5" (< 16.5 cm), Medium frame: 6.5" - 7.5" (16.5 - 19 cm), Large frame: > 7.5" (> 19 cm).
Women: Small frame: < 5.5" (< 14 cm), Medium frame: 5.5" - 6.5" (14 - 16.5 cm), Large frame: > 6.5" (> 16.5 cm).
These ranges account for natural bone structure differences. Frame size is independent of height and weight—a tall person can have a small frame, and a short person can have a large frame. Frame size reflects bone width and density, which affects optimal weight within the healthy BMI range.
- Frame Size Adjustment Logic:
Frame size adjustment applies ±10% to ideal weight formula results, creating personalized ranges:
Small Frame: -10% to -5% adjustment (targets lower end of ideal range). Example: If Robinson formula suggests 150 lbs, small frame range is 135-143 lbs.
Medium Frame: -3% to +3% adjustment (minimal change, near formula result). Example: If Robinson formula suggests 150 lbs, medium frame range is 146-155 lbs.
Large Frame: +5% to +10% adjustment (targets higher end of ideal range). Example: If Robinson formula suggests 150 lbs, large frame range is 158-165 lbs.
This adjustment acknowledges that bone structure affects optimal weight—larger bones can support more weight healthily, while smaller bones may be optimal at lower weights.
- Why Frame Size Matters:Frame size accounts for natural bone structure differences that affect optimal weight. Two people of the same height and gender can have different frame sizes, meaning their optimal weights differ even within the healthy BMI range. Small-framed individuals may be healthiest at the lower end of ideal weight ranges (BMI 18.5-22), while large-framed individuals may be optimal at the higher end (BMI 22-25). Frame size doesn't change the fundamental healthy BMI range (18.5-25) but helps personalize the target within that range. This is why frame size adjustment creates ranges rather than single numbers—it acknowledges that "ideal" weight varies based on individual bone structure.
The Impact of Aging on Ideal Weight
How Age Affects Ideal Weight Interpretation
- Age-Related Muscle Loss (Sarcopenia):Muscle mass starts declining around age 30, and it happens faster than most people realize—about 3-8% per decade. Here's what that means in practice: A 70-year-old who hits their "ideal weight" according to formulas might actually have 30% body fat, while a 30-year-old at the same weight has 20% body fat. Same weight, very different health status. Sarcopenia (the medical term for age-related muscle loss) affects your body composition way more than your total weight. That's why body fat percentage becomes increasingly important as you age. Ideal weight formulas can't see this—they only see the number on the scale. Maintaining muscle mass through strength training becomes critical for healthy aging, whether you're at "ideal weight" or not.
- How to Interpret Ideal Weight Formulas by Age:
Ages 18-30: Ideal weight formulas are most accurate during this period when muscle mass is typically stable. Body composition is more predictable, and formula results align well with health outcomes.
Ages 30-50: Muscle mass begins declining, but ideal weight formulas remain useful. Focus on maintaining muscle through strength training while managing weight. Consider body fat percentage alongside ideal weight.
Ages 50-65: Muscle loss accelerates, making body composition more important than total weight. Ideal weight formulas provide reference points, but body fat percentage and muscle mass become primary health indicators.
Ages 65+: Ideal weight formulas become less reliable due to significant muscle loss. Focus on body composition, functional strength, and maintaining muscle mass rather than just hitting a weight number. The healthy BMI range (18.5-25) remains valid, but body fat percentage is more critical.
- Maintaining Healthy Weight with Age:
As you age, maintaining "ideal weight" becomes less about the number and more about body composition:
Strength training: Essential for maintaining muscle mass and preventing sarcopenia. Aim for 2+ days/week of resistance training.
Protein intake: Older adults need more protein (1.0-1.2g per kg body weight) to maintain muscle mass.
Body composition monitoring: Track body fat percentage, not just total weight. Healthy ranges: Men 10-20%, Women 18-28%.
Functional fitness: Focus on maintaining strength, balance, and mobility rather than just weight.
Regular health monitoring: Work with healthcare providers to monitor body composition, muscle mass, and metabolic health. The goal shifts from "ideal weight" to "optimal body composition" as you age.
- When Ideal Weight Formulas Are Less Relevant:
Ideal weight formulas become less relevant when:
- You have significant muscle mass (athletes, bodybuilders)
- You're over age 65 (sarcopenia affects body composition)
- You have medical conditions affecting body composition
- You're pregnant or postpartum
- You have a history of eating disorders
In these cases, focus on:
- Body composition (body fat percentage)
- Functional strength and fitness
- Metabolic health markers (blood pressure, blood sugar, cholesterol)
- Consultation with healthcare providers for personalized guidance
Ideal weight formulas are tools, not absolutes—they provide reference points that should be interpreted in context of your overall health, body composition, and individual circumstances.
Ideal Weight vs. Healthy Weight: Understanding the Difference
Ideal Weight vs. Healthy Weight: What's the Difference?
- Ideal Weight Formulas (Single Numbers):Ideal weight formulas (Robinson, Miller, Devine, Hamwi) provide specific target weights, typically calculated for medical applications like drug dosing or clinical studies. These formulas produce single numbers (with frame size adjustments creating ranges). They're based on historical medical needs rather than modern health research. Formula results typically fall within the healthy BMI range (18.5-25) but may be more conservative or specific to medical applications. The variation between formulas (5-15 lbs) demonstrates that "ideal" weight is inherently subjective and context-dependent.
- Healthy Weight Range (BMI 18.5-25):Healthy weight is defined by BMI 18.5-25, representing the weight range associated with lowest risk of chronic diseases (Type 2 diabetes, cardiovascular disease, hypertension, certain cancers). This range is based on large-scale population studies showing optimal health outcomes. Healthy weight is a range, not a single number, acknowledging that optimal weight varies based on individual factors (frame size, muscle mass, age, genetics). The healthy BMI range is the modern standard for weight assessment, based on extensive research linking weight to health outcomes.
- How They Compare:
Ideal weight formula results typically fall within the healthy BMI range, but they represent different perspectives:
Medical perspective: Ideal weight formulas prioritize medical safety (drug dosing, clearance).
Health perspective: Healthy BMI range prioritizes disease prevention and longevity.
Specificity: Ideal weight formulas provide specific numbers, while healthy BMI range provides a broader range.
Application: Ideal weight formulas are useful for medical calculations, while healthy BMI range is useful for general health assessment.
Both concepts are valid but serve different purposes. The average of ideal weight formulas often aligns with the middle of the healthy BMI range (BMI 22-24), which research shows is optimal for longevity.
- Which Should You Use? (Spoiler: Both):Use ideal weight formulas when: You want to see how different historical formulas compare, you're curious about where these numbers came from (medical dosing vs. wellness), you need specific reference points for weight management discussions, you want to understand why "ideal" weight isn't one number. Use healthy BMI range when: You want the modern, research-backed standard for weight assessment, you're focused on disease prevention and longevity, you prefer a range over a single number, you're assessing overall health risk. Best approach: Use both. Seriously. Ideal weight formulas give you specific reference points and show you the variation between methods. Healthy BMI range gives you the broader health context and shows where ideal weight formulas fit. The average of ideal weight formulas usually falls right in the middle of the healthy BMI range (around BMI 22-24), which research shows is optimal for longevity. Frame size adjustments help personalize both approaches to your individual bone structure. Think of ideal weight formulas as "historical perspectives" and healthy BMI range as "modern standard"—they complement each other.