Easiest thing is to drain the fluid out of each fork and measure...as Glider says adding two much CAN blow seals and make fork too stiff, but 1 or 2oz over what you take out would probably not be overfilling. Measure them separately...you may be surprised to find out they may not be the same, but should be pretty close to 9-10oz...BTW I put in 9 oz in and used 7.5W Bel Ray and it was fine.