Dry Afromontane forests in Ethiopia are vital carbon sinks, yet accurate biomass and carbon stock assessments have been hindered by the lack of site-specific models. This study developed and validated multispecies allometric equations for Wof-Washa plantation and natural forests using biometric data from 127 trees across seven dominant species. Models incorporating diameter at breast height (DBH) and total height (H) explained up to 95% of aboveground biomass variation and outperformed pan-tropical models in accuracy and bias reduction. These findings provide robust tools for national carbon accounting and support sustainable forest management, contributing to climate mitigation and improved land-use planning in Ethiopia’s highland ecosystems.