One decibel change in loudness is equal to:
26 % change in intensity of sound
Since, L = 10 log10(I) dB, where 'L' is loudness and 'I' is intensity.
Now, L1 = 10 log10(I1) dB
L2 = 10 log10 (I2) dB
L2 - L1 = 10( log10(I2 ) - log10(I1 )) = 10 log10( I2I1 ) dB
Now if change in loudness is 1 dB, L2 - L1 = 1 dB
So, 10 log10( I2I1 ) = 1
⇒ log10( I2I1 ) = 110
⇒ I2I1 = antilog (0.1) = 1.26
Now % change = I2−I1I1 × 100 = 26 %