diff --git a/libraries/AP_Math/definitions.h b/libraries/AP_Math/definitions.h
index 44feadc48e..0f2c5d3b84 100644
--- a/libraries/AP_Math/definitions.h
+++ b/libraries/AP_Math/definitions.h
@@ -72,7 +72,9 @@ static const double WGS84_B = (WGS84_A * (1 - WGS84_F));
 static const double WGS84_E = (sqrt(2 * WGS84_F - WGS84_F * WGS84_F));
 #endif
 
-#define C_TO_KELVIN 273.15f
+#define C_TO_KELVIN(temp) (temp + 273.15f)
+#define KELVIN_TO_C(temp) (temp - 273.15f)
+#define F_TO_KELVIN(temp) C_TO_KELVIN(((temp - 32) * 5/9))
 
 #define M_PER_SEC_TO_KNOTS 1.94384449f
 #define KNOTS_TO_M_PER_SEC (1/M_PER_SEC_TO_KNOTS)