There is no pounds-per-hole number that is exact for every trailer. Values such as 250 pounds on a 4-inch rail or 400 pounds on a 6-inch rail are planning assumptions. Hole spacing matters, but it is not the only variable. Trailer geometry, suspension, fifth-wheel position, and where the freight sits also change the transfer.
Measure the load you have
Use two scale tickets and a known move. Suppose the first ticket shows 35,200 pounds on the drives and 32,800 on the trailer tandems. You move four holes forward. The reweigh shows 34,080 and 33,920. The drives lost 1,120 pounds and the trailer gained 1,120, so the observed transfer was about 280 pounds per hole.
Scale rounding, fuel burn, and small steer-weight changes can keep both sides from changing by precisely the same amount. CDLMath averages the drive and trailer changes and rejects a calibration when the numbers disagree enough to make the result unreliable.
Use the estimate correctly
A preset is useful for deciding the first move. The reweigh is what tells you how this trailer and load responded. Record the starting position, move whole holes, and keep the first ticket unchanged when entering the second one. If freight shifts or the setup changes, the old calibration may no longer describe the load.
The quick manual calculation is transferred weight divided by holes moved. Check both tandem groups: the amount removed from one should be close to the amount added to the other. If the drives change by 1,500 pounds but the trailer changes by only 700, do not average the numbers blindly. Recheck the tickets, fuel change, steer reading, and whether the move was recorded correctly.
Calibrate again when you switch trailers, the freight is reworked, or a later reweigh shows that the old estimate is no longer landing close. The measured number belongs to that setup and load, not to every trailer in the fleet.