# How do I convert coefficient values from 1/3 octave band to 1/1 octave band?

I have some coefficient values i.e. 74.9, 81.3, and 80.5 at frequency centers 63, 160 and 400 Hz. The values are 1/3 octave band values. I would like to convert them to the 1/1 octave band values. Can someone suggest how to do that?

If I'm understanding your question correctly, you want to sum up levels given as 1/3 octave bands into 1/1 octave band resolution. This can be accomplished by decibel summation:

$$L_\Sigma = 10 * log(10^\frac{L1}{10} + 10^\frac{L2}{10} + 10^\frac{L3}{10})$$

Where $$L$$ are levels in dB.

Please see here for an online summation tool.