Per 100 g and per serving are answering different questions
Every row in this checker carries two numbers that people mix up constantly: calories per 100 g (or per 100 ml for drinks and alcohol) and calories per natural serving. Per 100 g is a fixed ruler, the same amount of food every time, built for comparing one food against another regardless of how much of it anyone actually eats. Per serving answers a completely different question: how many calories are in the amount a person is realistically about to eat or drink.
Banana shows the gap at its gentlest. It runs 89 kcal per 100 g, but a single medium banana weighs about 118 g, so the serving figure comes out at 105 kcal, close to the per-100 g number because the two weights are close together. Crisps and watermelon show the same idea taken to an extreme. Ready-salted crisps sit at 532 kcal per 100 g, watermelon at just 30, nearly an eighteen-fold gap by that ruler alone. But a small bag of crisps weighs about 25 g (133 kcal), while a cup of diced watermelon weighs around 152 g (46 kcal), so the realistic serving gap narrows to under three-fold. Neither number is wrong. The per-100 g figure tells you which food is more energy-dense; the per-serving figure tells you what a normal portion of each actually costs. Reading only one of the two is how a food ends up seeming healthier, or worse, than it actually is next to whatever it is being compared with.
This is exactly why the panel above always shows both figures together, then adds a third: your portion, from the slider, recalculated the moment you move it. The formula behind every number on this page is short enough to print in full:
kcal for your portion = kcal per 100 g ÷ 100 × portion weight in grams kJ = kcal × 4.184
That second line matters too. Kilojoules are the SI energy unit and the one nutrition labels across the EU and UK are legally required to show alongside kilocalories; 4.184 kJ per kcal is the conversion factor those labels use, so the kJ figure here should match a supermarket wrapper for the same food, not just be a rough multiple.
Where these numbers come from
Every row is built from USDA FoodData Central, the same public nutrient database that underpins most nutrition labels and diet apps worldwide, and each row's source reference sits in the comparison table so you can check it yourself. Cooking method matters more than people expect: a boiled potato and a baked potato of the same weight are not the same number, which is why this checker lists them as separate rows rather than one generic "potato".
Published figures are typical values, not a guarantee for the exact item in your kitchen. Growing conditions, ripeness, brand formulation and portion size at the till all shift the true number a little in either direction, sometimes by ten percent or more for fresh produce. Treat every figure here as a solid, well-sourced estimate rather than a lab measurement of the specific banana on your counter.
Energy density, explained kindly
Energy density is simply calories per gram (or per 100 g, the same idea scaled up), and it is the single most useful idea for reading this checker sensibly. Watermelon is mostly water, so a plateful weighs a lot and delivers few calories. Crisps have almost no water and plenty of fat, the most calorie-dense macronutrient, so a small handful weighs little and delivers a lot. Two plates that look and feel similarly filling can differ by several hundred calories once you check the energy density behind each, which is precisely the comparison the category tables below make easy: sort any group by kcal per 100 g and the most energy-dense foods in it float straight to the top.
None of this is a verdict on any single food. Energy density is one honest fact about how a food is put together, useful for planning a plate, not a reason to avoid a food outright.
Reading the macro row
Alongside calories, every food carries protein, carbohydrate, fat and fibre in grams, each recalculated for whatever portion the slider is set to. Fibre is counted as part of total carbohydrate on the underlying data, the same convention used on a nutrition label, rather than added on top of it. The donut chart splits calories, not grams, between the three energy-carrying macros, so it visually reflects that a gram of fat carries roughly double the calories of the same gram of protein or carbohydrate; fibre contributes negligible usable energy and is left out of that split.
Questions people ask
Are these calorie counts exact for the food I am eating?
No single published figure can be, and this checker does not claim otherwise. It gives you a well-sourced typical value for that food and preparation method. Ripeness, brand, exact cut and cooking time all nudge the true number in either direction, usually by a small margin for whole foods and more for anything heavily processed.
Why do calories per 100 g and per serving look so different?
Because they answer different questions. Per 100 g is a fixed ruler for comparing foods regardless of portion; per serving reflects the actual weight of what most people eat in one go. A food can be very energy-dense per 100 g while still being modest per serving, if the serving itself is small, and the reverse is just as common.
What is energy density and why does it matter?
Energy density is calories per gram of food. Foods high in water and low in fat, like most fruit and vegetables, tend to be low in energy density: a large plateful can be a modest calorie count. Foods low in water and high in fat, like crisps or cheese, pack far more energy into the same weight. Sorting a category table by kcal per 100 g ranks that group by energy density directly.
Do the kJ figures match a UK or EU nutrition label?
They should. This checker uses the standard 4.184 kJ per kcal conversion that UK and EU nutrition labelling rules require, the same factor behind the kilojoule line on a supermarket wrapper, so the two should agree for the same food and portion.
Why are drinks and alcohol measured per 100 ml rather than per 100 g?
Liquids are conventionally measured by volume rather than weight, both on nutrition labels and in the source data, so those rows are built and labelled per 100 ml instead. The same maths applies: swap grams for millilitres and the portion slider works exactly the same way.
Can I compare foods from different categories?
Yes. The compare tray at the bottom takes up to three foods from anywhere in the list, search included, and lines them up by calories and protein per 100 g regardless of which category each one comes from.
What if the food I want is not in the list?
Use the suggest link next to the search box or under an empty search result. New foods get added in batches once there is a clear pattern of requests, so a specific, named suggestion is far more useful to us than a general one.
Figures on this page are typical published values for common preparations of each food, not a laboratory measurement of any specific item. This tool does not offer dietary or medical advice; anyone managing a medical condition through diet should work from figures checked with a registered dietitian or their own package labelling.