Unit converter
The four conversions this subject actually needs — bodyweight, height, food energy and water — instead of a hundred you don't.
The constants
1 lb = 0.45359237 kg exact 1 st = 14 lb 1 in = 2.54 cm exact 1 kcal = 4.184 kJ 1 floz = 29.5735295625 ml US
The pound and the inch are exact by international agreement — fixed by treaty in 1959, not measured — which is why a conversion should never disagree between two places. The app and this page share a set of generated test vectors precisely so they can't.
Why stone is shown as two numbers
Nobody in the UK says «12.9 stone» — they say «12 st 13». So stone renders as whole stones plus pounds, with 14 lb carrying up into the next stone rather than printing an impossible «12 st 14». The app does the same, and switches to plain pounds for weekly changes, because a «−0.02 st» chart axis is unreadable.
These are the same numbers and the same guards the Talk2Fit app applies when it builds your plan — the calculator is the app's own arithmetic, not a separate approximation.
Questions
Why does my food label say kJ instead of calories?
Because most of the world regulates energy in kilojoules — EU labels must print kJ, and Australia uses kJ almost exclusively. One kcal is 4.184 kJ, so an 8700 kJ 'average adult intake' on an Australian pack is about 2080 kcal.
Is a 'calorie' on a label the same as a calorie in physics?
No, and it is the single most common confusion here. Nutrition labels use the kilocalorie — 1000 physics calories. When a pack says 250 Calories with a capital C, it means 250 kcal. Everything on this site is kcal.
Which fluid ounce is this?
The US one, 29.5735 ml — the same as the app's water tracker. The imperial fl oz used in the UK is 28.41 ml, about 4 % smaller, which is enough to matter across a day of glasses.
Why is the pound 0.45359237 kg exactly?
Because it is defined that way, by international agreement since 1959, rather than measured. The site and the app both divide by that exact figure, so a weight you type in one never comes back different in the other.