Active vs total calories — three definitions, one unit
kcal is a unit, not a quantity. Three different numbers are reported in it, and
one major vendor does not use it at all.
The three definitions
| Definition | What it counts | Typical daily figure |
|---|---|---|
| Active | Energy above resting metabolism | 300–800 kcal |
| Total, including basal | Active plus what your body burns at rest | 2,000–2,800 kcal |
| Net / gross (dietary) | A food-logging convention about whether exercise is subtracted | varies |
The first two differ by a factor of three to five. Any comparison that does not establish which is which is comparing nothing.
The clearest illustration comes from one vendor
Oura reports both in the same record: active_calories and
total_calories. Same day, same device, same unit, and they are not the same
number.
In a data model that keeps only "calories, kcal", those two collapse into one field and the day reports whichever arrived last. That is not hypothetical — it is exactly what happens when energy is modelled by its unit instead of by its definition, and it is why our own model treats the definition as part of the measurement's identity rather than as a label.
The kilojoule trap
WHOOP reports energy in kilojoules. A day might read 8,400 kJ, which is about 2,000 kcal.
Read as kilocalories, 8,400 is a very big but not obviously impossible day — an ultramarathon figure. It does not trigger the "that cannot be right" reflex the way 84,000 would. That is what makes unit confusion worse than a unit error: the wrong number is plausible.
The general rule this illustrates: carry the vendor's own unit alongside every value and
convert in one place, rather than assuming a unit from the metric's name. A field called
calories tells you what is being measured and nothing about how it is expressed.
Why "just convert everything to kcal" is not the fix
Converting kJ to kcal is arithmetic and it is fine. Converting active to total is not — it requires a basal rate you do not have and cannot derive from the file. Unit conversion and definition conversion look similar and only one of them is possible.
What to compare
- Active against active, from the same device, over time.
- Total against total, likewise.
- Never active from one device against total from another, however close the numbers look.
The same reasoning applied to HRV is on SDNN vs RMSSD, and to vendor scores on recovery and readiness scores.