I am looking for a load for my 375 Ruger using a 235 grain Speer SSP bullet.

My 375 H&H uses 30.0 grains SR 4759 powder and gives MV of 1701 fps. (Based on the Speer Reloading Manual No. 13.)

I did a volume comparrison and the Ruger has 8% more volume than the H&H.
Anyone know how to calculate corresponding load for the Ruger. Would it be 8% more than the H&H 30 grains?

Bob the percentage increase is about half the volume increase.
Most of the SR4759 loads in the Speer manuals are intended to be be reduced loads so they do not operate anywhere near maximum pressure.
I normally pick the middle load for a starter and often just stick with it.

With the 375 Ruger you might used the middle load and when you are convinced it is mild go to the top H&H load.

If you are really concerned call Speer and check with them.