diff --git a/plugins/inputs/system/MEM_README.md b/plugins/inputs/system/MEM_README.md
index 9b766e700..16a0f7996 100644
--- a/plugins/inputs/system/MEM_README.md
+++ b/plugins/inputs/system/MEM_README.md
@@ -18,7 +18,7 @@ It is supposed to be used to monitor actual memory usage in a cross platform fas
 designed for informational purposes only.
 - **free**: memory not being used at all (zeroed) that is readily available; note
 that this doesn't reflect the actual memory available (use 'available' instead).
-- **used_percent**: the percentage usage calculated as `(total - used) / total * 100`
+- **used_percent**: the percentage usage calculated as `used / total * 100`
 
 ## Measurements:
 #### Raw Memory measurements: