I had testicle ultrasound performed some months ago. Here's my measurements:

Right testicle: 43 x 28 x 26 mm
Vol: 16.39 cc

Lest testicle: 45 x 23 x 25 mm
Vol: 13.55 cc

The formula for volume used was Pi/6 x length x width x depth. (If I used the 0.71 constant my volumes would be 22.2 cc and 18.37 cc)

My urologist said that my testicles were within average range but on the smaller side of the scale. Normal range is 12 to 35cc; average is 20cc.