SoilBenchRaised bed planning and fill math for real gardens.
Reference

Soil calculator for raised garden beds

Use cubic feet for bag math and cubic yards for bulk delivery. Switching between the two too late is where garden budgets start slipping.

Bed sizeDepthCubic feet1.5 cu ft bags
4 x 4 ft12 in1611
8 x 4 ft12 in3222
10 x 4 ft12 in4027
12 x 4 ft12 in4832