Getting the Most From a Ideal Weight Calculator: Tips and Common Errors

Updated 6 September 2026 · Health and fitness

A Ideal Weight Calculator gives a fast answer, but the answer is only as good as what goes in. These are the mistakes we see most often with ideal weight calculations in Australia, and how to avoid them.

1. Treating estimates as diagnoses

Formulas describe populations, not individuals. They can’t replace advice from a health professional.

2. Mixing kilojoules and calories

1 calorie equals about 4.2 kilojoules. Australian labels use kJ.

3. Relying on one measure

BMI, waist size and body fat each tell part of the story. Look at them together.

4. Underestimating drink sizes

Many pours and cans are more than one standard drink.

5. Overlooking the detail that matters most here

A healthy weight range is a guide, not a target. Body shape and muscle mass vary.

How the healthy BMI weight range changes with height

A common mistake is getting one input slightly wrong. Here is what happens to the healthy BMI weight range when “Height (cm)” is off by up to 20% in either direction, with everything else held steady.

Height (cm)	Healthy BMI weight range
140	36.3 to 48.8 kg
158	46.2 to 62.2 kg
175	56.7 to 76.3 kg
193	68.9 to 92.8 kg
210	81.6 to 109.8 kg

At 140 the result is 36.3 to 48.8 kg; at 210 it is 81.6 to 109.8 kg. If a small change in this input moves the answer a lot, it is worth double-checking that figure before you rely on the result.

A quick sense check

Healthy range = BMI 18.5 to 24.9 × height (m)². The Devine formula adds 2.3 kg per inch over five feet. With typical inputs the calculator returns healthy BMI weight range of 56.7 to 76.3 kg. If your own result looks wildly different, check that each figure is in the right unit and period (weekly, monthly or yearly) before drawing conclusions.