Everyday Numbers,
one multiplication at a time
Five calculators for the arithmetic that sits between everything else: converting a unit, splitting a total into parts, and turning a weekly or yearly figure into a daily one. Every page shows the step, not just the answer.
Most of these are one multiplication. The value is in showing which one.
Two people can split the same 2,400 calories 30/40/30 and end up four grams apart on protein — not because either is wrong, but because one rounded the calorie split before dividing by four and the other did not.
That is the whole reason this group exists. The arithmetic is not hard; the order is easy to get wrong, and the error is invisible afterwards because the result still looks like a number.
So each page states its inputs, shows the intermediate values, and rounds once at the end. Where a convention matters — four kilocalories per gram of protein and carbohydrate, nine per gram of fat, one hundred centimetres to the metre — the page names the convention instead of assuming you already know it.
None of these pages picks a target for you. They take a total you already have and do the division. If you do not have a total, there is nothing here to run — and that is deliberate.
Two groups, 5 calculators
Small on purpose. Each card is one calculation — the line under the name tells you what goes in and what comes out.
Unit Conversion
One conversion, done exactly. Metres to centimetres is a factor of one hundred — the page exists because people round before converting, not after.
Targets & Planning
Four calculations that take a total you already have and split it, or turn it into a per-day figure. None of them chooses the total for you.
Four steps, and the order matters more than the arithmetic
These pages share one rule: convert first, apply the ratio second, round last. Doing those in a different order produces a plausible number that is slightly wrong, which is the worst kind.
Fix the unit before anything else
Metres to centimetres, pounds to kilograms, weekly to daily — conversion happens first and at full precision. Converting a number you have already rounded bakes the rounding error in permanently.
Apply the ratio to the total, not to a rounded total
A 30/40/30 split of 2,400 kcal is 720, 960 and 720. Splitting “about 2,400” as three lots of 800 gives a different answer, and the difference survives every later step.
Convert energy to grams with the stated factor
Protein and carbohydrate at 4 kcal per gram, fat at 9. Fibre sits inside carbohydrate on US labels and outside it on EU labels, so each page says which convention it used rather than leaving you to guess.
Round once, at the end, and say so
Grams to whole numbers, percentages to one decimal. Rounding each intermediate value is how a split that should total 100% quietly arrives at 99.4%.
| Protein 30% | 720 kcal ÷ 4 = 180 g |
| Carbohydrate 40% | 960 kcal ÷ 4 = 240 g |
| Fat 30% | 720 kcal ÷ 9 = 80 g |
| Check back | 180×4 + 240×4 + 80×9 = 2,400 kcal |
The last row is the point of the page. If the grams do not multiply back to the total, one of the earlier steps was rounded too early.
Where the numbers come from
Four sources cover everything here — and one of them is you. Each page names the convention it applied, so a result can be reproduced by hand.
BIPM SI Brochure
Unit definitions and prefixes. A centimetre is one hundredth of a metre by definition rather than by convention, so that conversion carries no uncertainty at all. bipm.org
Atwater factors
4 kcal per gram for protein and carbohydrate, 9 for fat, 7 for alcohol. These are the rounded factors used on nutrition labels in both the US and the EU; the measured values are about 4.2, 4.2 and 9.4.
The total you supply
Calorie total, weekly figure, body weight — whatever the page divides. Nothing is defaulted to a recommended value, because a default would be a recommendation wearing a different hat.
kcal and kJ
One kilocalorie is 4.184 kilojoules exactly. Pages that show both convert once, at the end, so the two figures always agree with each other instead of drifting apart.
Six things that move the answer
None of these are mistakes in the arithmetic. They are choices, and each one changes the result by enough to notice.
- Rounding orderRounding an intermediate value can move a final total by one to two percent — small per meal, larger over a year of daily figures.
- Which gram factor4/4/9 against 4.2/4.2/9.4 changes the gram figures by up to five percent for the same calorie split.
- Fibre inside or outside carbohydrateUS labels count it inside total carbohydrate; EU labels list it separately. The same food can appear to have different carbohydrate totals.
- kcal against kJA factor of 4.184. A 2,000 kcal figure is 8,368 kJ — a number that looks like a different quantity but is not.
- Daily from weeklyDividing by seven gives an average, not a plan. Five days at 2,600 and two at 1,600 also average 2,314.
- Significant figuresA total quoted to two significant figures cannot support a result quoted to four. The pages keep the precision of the input, not more.
What these tools are not
Where a page is called “Protein Target” or “Macro Split”, the target is the one you typed. The calculator does not know your weight, your training, your age or your medical history, and it is not built to guess at any of them.
If a number matters for a health decision, the arithmetic on this page is the easy part. The input is the part worth discussing with someone qualified — a doctor or a registered dietitian has context this page cannot have.
Frequently asked questions
Why four calories per gram and not 4.2?
The measured values are about 4.2 kcal per gram for protein and carbohydrate and 9.4 for fat. Nutrition labels and most calculators use 4, 4 and 9 by convention, so that the grams multiply back to the stated calorie total. Using 4.2 makes each gram figure slightly lower and the split no longer adds up to the number you started with.
Should I work in kilojoules instead?
Only if your labels do. One kilocalorie is 4.184 kilojoules exactly. Converting mid-calculation adds a rounding step and gains nothing, so these pages convert once at the end when both units are shown.
Why does my app give a different macro split?
Three usual reasons: it rounded the calorie split before dividing, it used 4.2/4.2/9.4 instead of 4/4/9, or it counts fibre as part of carbohydrate where the EU convention does and the US one does not. All three conventions are named on these pages, so you can match whichever one you want.
Is the protein figure a recommendation?
No. It is your total calories, multiplied by the percentage you chose, divided by four. The page has no opinion about whether that percentage suits you, and it does not know your weight, training or medical history.
Why is there only one unit converter?
Because only one was needed often enough to build. The conversion factor is printed on the page, so everything else can be done by hand in one step — which is faster than loading a calculator for it.
Does rounding actually matter?
At the level of a single meal, no. Across a year of daily figures it does: a one percent rounding bias on 2,000 kcal is about 20 kcal a day, or roughly 7,300 over a year. That is why these pages round once, at the end, and show the unrounded intermediate values.
Who checks this, and what happens when a number is wrong
How this hub is maintained
- Every step is visible. Each page shows its intermediate values, not only the result, so the calculation can be checked by hand or reproduced in a spreadsheet.
- Conventions are named. Gram factors, unit definitions and the fibre convention are printed on the page. Where a choice exists, the page says which one it made.
- Corrections are welcome and acted on. If a result looks wrong, tell us the inputs you used and the convention you expected. We check it and correct the page rather than quietly adjusting the number. Contact the team.
- Reviewed on a schedule. Pages are re-checked when a definition or labelling convention changes and whenever a reader reports a discrepancy. The date above is the last full pass over this hub.
The other three groups
If what you need is not here, it is one of these.