--- title: "Calculating Dietary Energy" description: "Calculate and evaluate energy intake and requirements in a healthy daily diet, interpreting food labels and nutritional data" canonical: https://lightmysky.com/learn/science/calculating-dietary-energy-mt_83KkBCtVyR source: https://lightmysky.com/learn/science/calculating-dietary-energy-mt_83KkBCtVyR.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Calculating Dietary Energy Calculate and evaluate energy intake and requirements in a healthy daily diet, interpreting food labels and nutritional data Subject: Science · Area: Organisms & Life Processes · Ages 11 to 13 Page: https://lightmysky.com/learn/science/calculating-dietary-energy-mt_83KkBCtVyR ## Ready when they can - Reads and interprets a nutritional information label (kJ and kcal) - Estimates daily energy requirements for a person of a given age/activity level - Compares the energy content of different diets and identifies surpluses or deficits ## Lesson: Calculating dietary energy Food labels list more than ingredients. They also show energy, the fuel your body gets from food. Energy is measured in two units: kilojoules (kJ) and kilocalories (kcal). On labels, kcal is often just called Calories. kJ and kcal measure the same energy, just in different sized units. One kcal is about 4 kJ, so the kJ number on a label is always roughly four times bigger than the kcal number. *(drawing: Each bar shows the energy in one breakfast, in kcal. Taller bar, more energy.)* **Example.** A chocolate bar label says: Energy 800 kJ, 200 kcal per bar. Maya checks the numbers: 200 kcal times 4 is about 800 kJ. They match, so she trusts the label. **Tip.** Everyone's daily energy need is a bit different. It depends on your age, size and how active you are. A rough guide for someone your age is about 2000 kcal a day, more if you train hard. Add up the kcal in your meals and snacks, then compare the total to your daily guide to spot a surplus or a deficit. **Recap.** Read the kJ and kcal on the label, add up a day's meals, and compare the total to your daily energy guide. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Nutrients in a Healthy Diet](https://lightmysky.com/learn/science/nutrients-in-a-healthy-diet-mt_sDmrVCfzqt) ## Opens up - [The Digestive System and Testing Food for Nutrients](https://lightmysky.com/learn/science/the-digestive-system-and-testing-food-for-nutrients-mt__mBJCQEqPS)