Implementations described herein contemplate measuring the carrier phase (CP) of carrier signals transmitted by constituent satellites of a Global Navigation Satellite System (GNSS) to provide highly accurate calculations of a gradient of a road segment between different points at which the vehicle received carrier signals (from which CP measurements were made). The methods described herein are able to calculate the road grade with only an approximate estimate of the absolute altitude of the receiver. Similarly, the methods described herein are able to provide a precise estimate of road grade with only an approximate estimate of the absolute value of latitude or longitude. Furthermore, implementations described herein provide highly accurate calculations of road grade information with standard GNSS vehicle hardware and are thereby able to achieve a substantial increase in accuracy without increasing cost.