How to Use Fitness Calculator Results
Updated · MetaSys Limited
Check the units, understand what is being estimated, and treat the result as information rather than an instruction.
Choose the tool for your question
| Tool | What it estimates | What it cannot tell you |
|---|---|---|
| BMI | Weight relative to height | Body fat, muscle mass or a diagnosis |
| BMR | Resting energy needs using a population equation | A recommended food intake |
| TDEE | Daily energy use after an activity multiplier | Your measured individual metabolism |
| Macros | A selected allocation of calories to nutrients | An individually prescribed nutrition plan |
Check units before interpreting a number
A height of 170 means very different things in centimeters and inches. Re-enter values after switching units if necessary and check the selected unit labels. Body weight varies during the day; a single measurement can also be affected by hydration, clothing and measurement technique.
A worked example
For an illustrative adult weighing 70 kg and measuring 1.75 m, BMI is 70 ÷ (1.75 × 1.75) = 22.9 kg/m² after rounding. This describes weight relative to height. It does not reveal how much of that weight is muscle or fat. Adult category boundaries must not be applied to children.
Why estimates disagree
Different equations were developed using different populations and assumptions. A daily-energy estimate adds uncertainty from activity classification to uncertainty in resting-energy prediction. A more detailed result display does not remove those uncertainties. Compare the assumptions before comparing the numbers.
Use patterns, not false precision
Training, nutrition and health decisions require more context than a webpage can collect. When a number will affect a treatment or a substantial change in diet or exercise, discuss it with an appropriately qualified professional. Children, pregnancy, breastfeeding and medical conditions need particular care.
Find the method and its limitations
Read the explanation on the calculator page, then check Methodology & Sources and our Medical Disclaimer. For BMI interpretation, see the CDC’s BMI explanation. For the resting-energy equation used here, see Mifflin and colleagues’ original study.