01
The basic formula
Pool = (daily outbound loads × buffer days) + inbound trailers waiting to unload + 1 spare. A plant shipping 4 loads a day with a one-day buffer and one inbound on the ground needs about 6 trailers.
02
Choosing the buffer
One day of buffer lets loading run a shift ahead of pickups. Two days covers Monday surges and Friday cut-offs. More than two usually means the swap cadence is too slow, not that you need more trailers.
03
Account for peaks
Look at the busiest week of the last quarter, not the average. If peak is 40% above average, either size to peak or agree on surge trailers the carrier can add within a day.
04
Yard constraints
Count real parking positions with room to back in, not total square feet. A pool the yard cannot hold creates its own dwell problem.
05
Review on data
Trailer GPS shows dwell per unit. If several trailers sit unmoved for days, the pool is oversized; if loading routinely waits for an empty, it is undersized. Re-size quarterly.