This paper presents heterogeneity ratio (HR) as a new routing metric for heterogeneous MANETs. This metric is the ratio of number of powerful nodes to hop count that is used to select the best path to destination. Node heterogeneity is modeled in terms of: types and number of different interfaces, power, and transmission ranges. Our proposed routing metric is based on developing route discovery algorithm that is implemented on the top of on-demand tree-based routing protocol (OTRP) to accommodate nodes heterogeneity. Simulation results show that using HR with OTRP heterogeneity aware outperforms other metrics like minimal hop count and maximal number of powerful nodes.