The FDA standard measurement for gluten is PPM (parts per million), which is the measurement of concentration of a solution. 1 ppm is one part by weight, or volume, of solute in 1 million parts by weight, or volume, of solution.
For example, take two glasses of orange juice. One glass is 8oz with 20ppm of gluten and one glass is 16oz with 9ppm of gluten. To find the end concentration of gluten, you will need to find the new ratio of gluten to volume. It is not as simple as adding a volume together, as PPM is a unit of concentration.
(8oz x 20ppm) + (16oz x 9ppm) =
(160) + (144) = 304
8oz + 16oz = 24oz total volume
304/24 = 12.666 ppm gluten concentration of the new 24oz volume.
This would be similar to mixing two different pizza doughs; one with low gluten concentrate and one with high. You wouldn't add the low gluten pizza dough to the other pizza dough to increase the overall gluten concentrate. You would need to add the actual substance alone (gluten), to increase the overall concentration.
https://sciencing.com/calculate-concentration-solution-different-concentrations-8680786.html This article goes into more detail of what I explained above.