The 530 × 325 mm of a GN 1/1 pan is its rim size under EN 631-1; on models with handles these can project beyond it. Fit in a container is worked out by comparing this size with the interior width and depth.

Isotec TBXInterior width × depthGN 1/1 per shelf
725604 × 809 mm2 (325 × 2 = 650 mm depth)
900611 × 1025 mm3 (325 × 3 = 975 mm depth)

The remaining margin goes to the handles, the shelf rails and keeping the pan from moving in transit. Deep pans (100-200 mm) hold more food but widen the shelf spacing, while shallow pans give more shelves.