Highlights • New allometric equations were developed for predicting aboveground and belowground biomass (AGB and BGB) of trees and multi-stemmed shrubs in the Guinean savannas based on field measurements, providing information for West African mesic savannas and filling a critical knowledge gap. • AGB and BGB of trees were better predicted from the quantity ρD b 2 H (with ρ the specific wood density in g cm-3 , D b the stem basal diameter in cm, and H the tree height in m). • Obtaining accurate estimates of AGB and BGB in multi-stemmed shrubs required additional consideration of the total number of stems. • The root/shoot biomass ratio decreased with increasing of the stem size (measured by D b) for trees but remains relatively unchanged for shrubs.