diff --git a/docs/devices/Sonoff-S31.md b/docs/devices/Sonoff-S31.md
index b5c8484f60..37b9d48401 100644
--- a/docs/devices/Sonoff-S31.md
+++ b/docs/devices/Sonoff-S31.md
@@ -26,3 +26,6 @@ Tinkerman's review of [Sonoff S31](http://tinkerman.cat/sonoff-s31-now-serious/)
 
 ### Video tutorial by Robert Cowan
 [![](https://youtu.be/IvfiLcHMekQ "")
+
+### Prometheus power metrics units
+When enabled, the prometheus exporter will report `energy_power_kilowatts_daily` and `energy_power_kilowatts_total` metrics. While the naming convention implies that the metrics' values are measured in kilowatts, they are in fact measurements of kilowatt _hours_.