Which IBW formula should I use?

For fitness and weight management goals, present all three alongside the healthy BMI weight range and let the range speak for itself. For clinical drug dosing, Devine is the most widely used formula in Australian and US healthcare settings.

What if the client is very muscular and heavier than IBW?

IBW does not account for muscle mass. A highly trained athlete 10 kg over IBW may be in excellent health. Use body fat percentage as a more meaningful goal: target 10-18% for athletic males, 18-25% for athletic females.

What is a realistic rate of progress toward IBW?

A sustainable rate is 0.5-1.0% of body weight per week -- roughly 0.4-0.8 kg/week for an 80 kg person. Faster rates increase muscle loss risk. Use the Target Date Calculator to show the client how long a safe approach will take.

Ideal Body Weight (IBW) — Free Fitness Calculator

🎯

Client asks 'what should I weigh?' at the end of the session. You have their height. You need a range -- not a single number -- and the clinical reasoning before the next client arrives.

Ideal Body Weight (IBW)

Assessment

Height (cm)

Imperial: enter inches

Sex

Devine (M): 50 + 2.3 × (inches over 5ft) Devine (F): 45.5 + 2.3 × (inches over 5ft) Devine (1974) is the most widely used — originally developed for drug dosing. Robinson (1983) and Hamwi (1964) offer alternative estimates. Use healthy BMI range as a practical target for fitness goals.

Reference: Devine BJ — Drug Intelligence 1974 · Robinson JD — Am J Hosp Pharm 1983

ℹ️ Results are estimates for planning purposes. Verify with current standards and a qualified professional.

1 What this calculator does

Calculates Ideal Body Weight (IBW) using three validated clinical formulas -- Devine (most widely used), Robinson and Hamwi -- plus the healthy BMI weight range. Provides a realistic target range rather than a single number.

2 Formula & professional reasoning

Devine (1974): Male = 50 + 2.3 x (inches over 5 ft) | Female = 45.5 + 2.3 x (inches over 5 ft)
Robinson (1983): Male = 52 + 1.9 x (inches over 5 ft) | Female = 49 + 1.7 x (inches over 5 ft)
Hamwi (1964): Male = 48 + 2.7 x (inches over 5 ft) | Female = 45.5 + 2.2 x (inches over 5 ft)
Healthy BMI range: 18.5 to 24.9 x height (m)^2

IBW formulas were originally developed for drug dosing in clinical settings -- they give a height-based reference weight independent of the patient's actual weight. Devine is the most cited in pharmacokinetics and critical care. All three formulas use inches-over-5-feet as the height variable, which is why results for people shorter than 152 cm should be interpreted cautiously. The healthy BMI weight range (18.5 to 24.9 x height^2) is the most practical target for fitness and weight management.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Average height male

Given: Sex: male | Height: 175 cm (69 inches) | Inches over 5 ft: 9

Working:

Devine: 50 + (2.3 x 9) = 70.7 kg | Robinson: 52 + (1.9 x 9) = 69.1 kg | Hamwi: 48 + (2.7 x 9) = 72.3 kg | BMI range: 56.6 to 76.2 kg

Answer: IBW 69-73 kg range | Healthy BMI weight: 56.6-76.2 kg

💡 The three formulas agree well at average height. The healthy BMI range is broader and most practical for fitness goal-setting.

Standard

Female client -- realistic target

Given: Sex: female | Height: 163 cm (64 inches) | Inches over 5 ft: 4

Working:

Devine: 45.5 + (2.3 x 4) = 54.7 kg | Robinson: 49 + (1.7 x 4) = 55.8 kg | Hamwi: 45.5 + (2.2 x 4) = 54.3 kg | BMI range: 49.2-66.3 kg

Answer: IBW 54-56 kg range | Healthy BMI: 49-66 kg

💡 If the client currently weighs 72 kg, IBW formulas suggest 16-18 kg loss. Discuss whether this is realistic or whether a functional goal (e.g. BMI 23-24) is more achievable and sustainable.

Advanced

Tall individual -- formula divergence

Given: Sex: male | Height: 193 cm (76 inches) | Inches over 5 ft: 16

Working:

Devine: 50 + (2.3 x 16) = 86.8 kg | Robinson: 52 + (1.9 x 16) = 82.4 kg | Hamwi: 48 + (2.7 x 16) = 91.2 kg | BMI range: 68.9-92.7 kg

Answer: IBW range 82-91 kg | Healthy BMI: 69-93 kg

💡 At extreme heights the formulas diverge. Use the BMI healthy range as the practical target. The wide range (69-93 kg) reflects that body composition matters far more than a single scale number.

4 Sanity check

IBW formulas are clinical, not fitness, tools

Originally designed for drug dosing -- not weight management targets

A lean athletic 80 kg person at 180 cm is healthier than a sedentary 68 kg person at the same height.

Devine formula works best for

Height 152-180 cm | Not validated for heights under 152 cm

For people under 152 cm, use healthy BMI weight range instead.

Practical fitness target

Aim for the lower half of healthy BMI range (18.5-22) for most clients

BMI 22-23 is a realistic and achievable first target for most overweight clients.

Frame size adjustment

IBW formulas do not account for frame size -- large frames may naturally be 10-15% higher

5 Common errors

Error	Cause	Consequence	Fix
Presenting IBW as a precise goal weight	Treating formula output as a definitive target	Client demoralised if the target seems impossibly low, or confused by conflicting formula results	Always present IBW as a range and explain it is a clinical reference point. The healthy BMI weight range is more appropriate for goal-setting.
Using IBW for clients under 152 cm	Applying inches-over-5-feet formula when height is below 5 feet	Negative or nonsensical IBW result from Devine formula	For clients under 152 cm, use only the healthy BMI weight range (18.5-24.9 x height^2).
Not considering body composition when setting weight goals	Focusing on scale number alone	Client reaches IBW at low muscle mass -- 'skinny fat' -- with poor metabolic health	Pair IBW with a body composition target. A client 5 kg over IBW with good muscle mass is often healthier than someone at exactly IBW with low muscle.
Mixing Devine, Robinson and Hamwi for clinical drug dosing	Not confirming which formula the prescriber uses	Significant dosing error for weight-adjusted medications	For drug dosing (vancomycin, gentamicin) confirm which IBW formula your institution uses. Devine is most common in Australian hospitals.