BMR Calculator: Formula, Example and What the Result Means
Estimates the energy your body uses at rest, in kilojoules and calories. This guide walks through what each input means, the formula behind the answer and a worked example using typical Australian figures. You can follow along in the free BMR Calculator.
Why it matters
Australian nutrition labels use kilojoules, alcohol is measured in standard drinks of 10 grams, and health guidance comes from sources such as the NHMRC and Healthdirect. These calculators use common, published formulas as a starting point.
What you need to enter
The calculator asks for 4 inputs. The table shows each one with the example value used later in this guide.
| Input | Example value |
|---|---|
| Weight (kg) | 75 |
| Height (cm) | 175 |
| Age | 35 |
| Sex (1 = male, 0 = female) | 1 |
The formula
Mifflin-St Jeor: 10 × weight + 6.25 × height − 5 × age + 5 (men) or − 161 (women). 1 kcal = 4.184 kJ.
Worked example
Entering the example values above gives these results:
| Result | Value |
|---|---|
| BMR | 7,003 kJ per day |
| In calories | 1,674 kcal per day |
The headline figure is 7,003 kJ per day (BMR). Change any input in the calculator and every result updates instantly, so you can test different scenarios side by side.
How the BMR changes with weight
The table below keeps every other input at the example value and moves only “Weight (kg)” up and down by 10% and 20%. It shows how sensitive the BMR is to that one figure.
| Weight (kg) | BMR |
|---|---|
| 60 | 6,375 kJ per day |
| 68 | 6,710 kJ per day |
| 75 | 7,003 kJ per day |
| 82 | 7,296 kJ per day |
| 90 | 7,631 kJ per day |
At 60 the result is 6,375 kJ per day; at 90 it is 7,631 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 practical tip
Australian food labels use kilojoules, so the kJ figure is easiest to compare with what you eat.
Keep going
Before relying on the number, read BMR: What to Check Before You Trust the Number. You might also find these guides useful:
- Using a Daily Kilojoule Needs Calculator in Australia: A Step-by-Step Guide
- Body Fat Calculator Explained for Australians
- How the Ideal Weight Calculator Works (With a Worked Example)
Frequently asked questions
- Are these calculators medical advice?
- No. They provide general information. See your GP or visit healthdirect.gov.au for personal advice.
- Do they work for children?
- No. Adult formulas are used throughout. Children’s growth is assessed differently.
- Where do the formulas come from?
- Each calculator page names the formula used, such as Mifflin-St Jeor for BMR or the US Navy method for body fat.
Run your own numbers in the BMR Calculator.
Open the calculatorGeneral information only. Rates and thresholds change, usually on 1 July. Confirm current figures with the ATO or the relevant authority, and get personal advice for decisions about your situation.