Calories and macros: the basics

1 June 2026

A short, practical explainer. No heavy theory — just enough to understand the numbers in an app like noots.

What is a calorie?

A calorie (kcal) is a measure of energy. Food provides energy; movement and your metabolism burn it. Take in roughly as much as you burn over time and your weight stays stable. Consistently less → you lose weight. Consistently more → you gain. That’s the principle; the execution is harder, because every number is an estimate.

The three macros

“Macros” are the three building blocks in your food that provide energy:

Protein — for repair, muscle and feeling full. About 4 kcal per gram.
Carbohydrates — your main, fastest fuel. About 4 kcal per gram.
Fat — energy, vitamin absorption and hormones. About 9 kcal per gram — more than twice as energy-dense as the other two.

(Alcohol, by the way, is about 7 kcal per gram, but isn’t counted as a macro.)

Those numbers — 4, 4 and 9 — come from the Atwater system and are averages. They explain why a tablespoon of oil has so many calories: fat is simply concentrated energy.

How much of each macro?

There’s no perfect ratio for everyone. The widely accepted ranges (the Acceptable Macronutrient Distribution Ranges) are:

Carbohydrates: 45–65% of your calories
Fat: 20–35%
Protein: 10–35%

A lot is possible within those margins. People who train or want to keep muscle often aim for more protein (frequently around 1.2–2.0 grams per kilo of body weight). But treat it as a guideline, not a rule.

carbs 50% 45–65% recommended
protein 20% 10–35% recommended
fat 30% 20–35% recommended

An example split, within the widely recommended ranges.

How to think about it practically

You don’t need to memorise this or do the maths. noots works out the calories and the macros from what you write down, and shows your protein, carbs and fat at a glance. Handy to check whether you’re getting enough protein, without a calculator.

Above all: the numbers are a tool to get a sense of things, not an exam. Want to know how many calories you need per day? Read the guide How many calories do you need per day?.