diff --git a/lib/xmet/thermo.py b/lib/xmet/thermo.py
index 4228bfe..23acabb 100644
--- a/lib/xmet/thermo.py
+++ b/lib/xmet/thermo.py
@@ -55,4 +55,4 @@ def lapse(temp: float, rate: float, delta: float) -> float:
     Return the temperature of a parcel cooled at either the dry or moist lapse
     rate for a given increase in height (in meters).
     """
-    return temp - (rate * (delta / 1000))
+    return temp - (rate * delta)