Home / Energy balance
The library
Everything we know about energy balance, in one place.
The guides below were written for an Australian audience in kilojoules. We have kept the arithmetic and added the calorie beside every figure, because they are the same quantity written in a different unit.
Both units, always
1 cal ≈ 4.2 kJ
2,000 cal = 8,400 kJ, the US label reference day
Start here
Understand energy
What the unit is, what a day of it looks like, and how the two sides of the bar actually behave.
6 guides
What is a kJ?
The unit, defined in plain language, with the calorie conversion you actually need.
kJ Explained
Why food labels use kilojoules, what the number is measuring, and what it is not telling you.
Balance and Burn
How energy in and energy out settle against each other over weeks rather than days.
How many kJ does the average person need?
Where the 2,000 calorie label reference comes from, and why an average is a poor description of any one person.
kJs and You
Age, size, sleep and activity all move your number. What shifts it, and by roughly how much.
Your Ideal Figure
Working out a daily figure that fits your body, without turning it into a rule to fail against.
Energy in
Food
What is in the things you already eat, stated plainly rather than judged. There are no good foods or bad foods here.
4 guides
kJs in Food
How energy density works, and why two plates of the same size can be very different numbers.
Kilojoules in Common Foods
A lookup table for everyday staples, in kilojoules and calories side by side.
Fast Facts on Fast Food
What a typical drive-through meal adds up to, and what that means against an average day.
Guess How Many kJs These Foods Have
A short self-test. Most people are confidently wrong in both directions, which is the point.
Energy out
Movement
What activity actually returns on the bar, and the better reasons to do it anyway.
4 guides
How to burn your kJs
The honest arithmetic on exercise: how much movement a given amount of food energy really equals.
kJ Activity Comparison
Walking, swimming, cycling, gardening and cleaning, compared per half hour, in both units.
Get Active
Building movement into a week that is already full, without joining anything.
Take the Stairs
The small, unglamorous movements that add up quietly across a day.
For families
Kids
How to talk about food energy with children without handing them a diet, or a fear of the label.
4 guides
kJs and Kids
Why a growing body is not a smaller adult body, and why the same rules do not transfer.
Explaining kJs to Kids
Language that works at the dinner table: energy as fuel, not as reward or punishment.
How many kJ’s do kids need
Rough figures by age, in kilojoules and calories, and why the range is so wide.
Activities for Kids
Movement that children will actually repeat, which is the only kind that counts.
The toolbox
Tools, Tips, and Links
Calculators, conversion tables and the outside references we lean on, collected in one place so you don’t have to trust a number just because it appeared on a website.
A note on where these came from
This library was written for readers who buy food labeled in kilojoules. We have not rewritten the science to suit a US audience. We have simply put the calorie next to the kilojoule everywhere, so you can read it in whichever unit your brain already thinks in.