Skin temperature on wearables: absolute vs deviation
Updated
Short answer
Some wearables report skin temperature as an absolute value in °C, and others report it as a deviation from your own recent baseline. They are different quantities. They cannot be plotted on one axis, and neither can be turned into the other.
Skin temperature is not body temperature
A wearable measures the temperature of the skin where it sits, on a finger or the wrist, not the temperature at the core of the body. Skin temperature moves with the room, with blankets, with where the sensor sits and with blood flow, so a single absolute reading says little by itself. That is one reason several devices report the change from your own baseline instead.
Absolute value and deviation
| Kind | What the number is | Example |
|---|---|---|
| Absolute | The measured skin temperature, in °C or °F | Whoop's API reference lists a skin_temp_celsius value |
| Deviation | How far the night's temperature was from your own recent baseline, in °C or °F | Oura says it reports skin temperature as a change from your baseline |
A deviation of +0.3 °C means 0.3 degrees above your own baseline, whatever that baseline is. An absolute reading of 33.8 °C is a temperature on its own. The two answer different questions, so a trend in one cannot be read off the other.
What this means for tracking
- Keep them separate. BiomarkerHQ stores skin temperature (absolute) and skin temperature deviation as two different series and never draws them on one axis.
- Do not compare across devices. Different devices use different sensors, sites and baselines, so one device's deviation is not comparable with another's.
- Compare a device with its own history. A trend from the same device is the meaningful comparison.
Converting Fahrenheit
Some exports use °F. An absolute temperature converts with an offset. A deviation is a difference between two temperatures, so the offset cancels and it converts with the ratio alone.
absolute: °C = (°F − 32) × 5 ÷ 9
deviation: Δ°C = Δ°F × 5 ÷ 9
Frequently asked questions
Is skin temperature the same as body temperature?
No. A wearable measures the skin where it sits, not the core of the body, and skin temperature moves with the surroundings. It is a different measurement from a thermometer reading.
How do I convert a temperature deviation from °F to °C?
Multiply by 5 ÷ 9 and do not subtract 32. A deviation of +1.0 °F is about +0.56 °C.
Can I compare Oura's temperature with Whoop's?
Not directly. One reports a deviation from your baseline and the other an absolute value, and the sensors and baselines differ. BiomarkerHQ keeps them as separate series.
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