diff --git a/libraries/AP_Math/definitions.h b/libraries/AP_Math/definitions.h
index ea9e1a6c5c..89a44c3256 100644
--- a/libraries/AP_Math/definitions.h
+++ b/libraries/AP_Math/definitions.h
@@ -74,6 +74,9 @@ static const double WGS84_E = (sqrt(2 * WGS84_F - WGS84_F * WGS84_F));
 #define C_TO_KELVIN 273.15f
 
 #define M_PER_SEC_TO_KNOTS 1.94384449f
+#define KNOTS_TO_M_PER_SEC (1/M_PER_SEC_TO_KNOTS)
+
+#define KM_PER_HOUR_TO_M_PER_SEC 0.27777778f
 
 // Gas Constant is from Aerodynamics for Engineering Students, Third Edition, E.L.Houghton and N.B.Carruthers
 #define ISA_GAS_CONSTANT 287.26f