How to calculate it yourself
Dry-pack volume (ft³) = pan area × average mud thickness in feet. Pre-slope thickness averages ½–1 inch (¼" per foot of run from the drain). Final mud bed averages 1¼–1½ inches. Total avg thickness = 1¾–2½ inches across the whole pan. One 80 lb bag of sand-topping mix yields 0.6 ft³.
Common scenarios
Standard 3×5 ft shower pan (most common)
Pre-slope: 0.85 ft³ + final bed: 1.65 ft³ = 2.5 ft³ total = 4 bags of 80 lb sand-topping ($24-36 in materials). Mix small batches; dry pack is workable for only 30-45 minutes once mixed.
Curbless / zero-entry shower (4×5 ft)
2.67 ft³ total = 5 bags. Curbless designs need extra attention to slope (closer to ⅜" per foot toward the linear drain) — order one extra bag for grading adjustments.
Steam shower with bench (5×5 ft + bench mortar)
Floor: 6 bags. Bench top mud bed: 1-2 extra bags depending on bench size. Plus thinset on top to set the tile. Total dry-pack budget: $50-65.