增加一倍 = doubled (×2), but
是...
的一倍 technically means 'is one time as much as', so in Chinese A
是B
的一倍 = A equals B (same amount) in strict usage, though many speakers use it loosely to mean 'twice as much'. Safer: use
两倍 (liǎngbèi) for 'twice' when comparing.