The best form factor of three fast growing tree species Corymbia citriodora, Khaya senegalensis and Casuarina equisetifolia growing in Serapium Plantation, Ismailia Governorate, Egypt were calculated. Real form factor (ƒr) was calculated and its value was statistically compared to values of Natural (ƒ0.1), Artificial (ƒ0.5), Hohenadl's (ƒh), Girard (ƒg), and Absolute (ƒa) form factors using a paired t-test analysis . Also, real volume was measured and compared to volume calculated with different form factors.  Results showed that (ƒr) can be replaced by (ƒh) , (ƒ0.1) and (ƒa) in Corymbia citriodora and Khaya senegalensis. Whereas, (ƒ0.1) and (ƒa) form factors can be used instead of (ƒr) in Casuarina equisetifolia. In addition, results showed no significant differences between real volume and volumes derived from different form factor equations.