BMR: What to Check Before You Trust the Number

Updated 3 September 2026 · Health and fitness

A BMR 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 BMR calculations in Australia, and how to avoid them.

1. Mixing kilojoules and calories

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

2. Relying on one measure

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

3. Underestimating drink sizes

Many pours and cans are more than one standard drink.

4. Treating estimates as diagnoses

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

5. Overlooking the detail that matters most here

Australian food labels use kilojoules, so the kJ figure is easiest to compare with what you eat.

How the BMR changes with height

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

Height (cm)	BMR
140	6,088 kJ per day
158	6,558 kJ per day
175	7,003 kJ per day
193	7,474 kJ per day
210	7,918 kJ per day

At 140 the result is 6,088 kJ per day; at 210 it is 7,918 kJ per day. 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

Mifflin-St Jeor: 10 × weight + 6.25 × height − 5 × age + 5 (men) or − 161 (women). 1 kcal = 4.184 kJ. With typical inputs the calculator returns BMR of 7,003 kJ per day. 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.