Mortar Calculator — Thinset, Mud Bed & Shower Pan Takeoff

Mortar for tile work is almost always thinset — the cementitious adhesive that holds the tile to the substrate. The amount depends entirely on the notch size you choose, which in turn depends on the tile format. Here are the five standard doses: 3/16 in V-notch (glass mosaic) → 0.22 lb/ft², 1/4 in V-notch (small wall tile) → 0.28 lb/ft², 1/4 × 1/4 in square (standard floor) → 0.53 lb/ft², 1/4 × 3/8 in square (plank) → 0.67 lb/ft², and 1/2 × 1/2 in square (large format) → 0.91 lb/ft². Multiply your area by the lb/ft², add 10% for pot-life waste, then divide by 50 lb per bag and round up. A 200 ft² standard floor needs 200 × 0.53 × 1.1 = 117 lb → 3 bags.

Coverage figures are tied to the notch because the notch sets the mortar bed thickness. A 50 lb bag of polymer-modified thinset covers roughly 225 ft² with a 3/16 in V-notch (glass mosaic), 180 ft² with a 1/4 in V-notch (small wall), 95 ft² with a 1/4 × 1/4 square (standard floor), 75 ft² with a 1/4 × 3/8 square (12 × 24 plank), and 55 ft² with a 1/2 × 1/2 square (24 × 48 large format). All assume a flat slab with full ridge collapse. Out-of-flat slabs reduce coverage — a slab out of flat by 1/4 in per 10 ft cuts all these figures by about 20%.

They are the same product applied in different places and different thicknesses. Dry pack mortar (4:1 cement-to-sand by volume) is deck mud when used to build a shower pan floor to slope — typically 3/4 to 1-1/2 in thick, compacted in lifts no thicker than 4 in. Floor mud is the same mix used to create a flat subfloor over an uneven slab — typically 1/2 to 2 in thick. The ratio is 4 volumes of clean masonry sand to 1 volume of Portland cement. Mix it damp — the texture of packed beach sand, not wet like concrete. Deck mud for shower pans compacts with a tamping tool; floor mud screeds flat over the substrate.

A typical 36 × 60 in shower pan needs about 1.2 cubic feet of dry pack mortar. Here is the calculation: area = 36 × 60 ÷ 144 = 15 ft². Slope = 1/4 in per foot of run. The pan drains toward the center, so average depth = curb height (typically 2 in) minus half the slope drop. For a 2 ft run to center, slope drop = 2 × 1/4 = 0.5 in. Average depth = 2 - 0.25 = 1.75 in = 0.146 ft. Volume = 15 × 0.146 = 2.19 ft³ gross. Subtract pipe and drain footprint ≈ 0.2 ft³. Add 10% compaction loss ≈ 0.2 ft³. Total ≈ 2.19 ft³. Round up to 2.5 ft³ to cover over-dig. 4:1 ratio means 0.5 ft³ of cement (one 94 lb Portland bag) and 2.0 ft³ of sand.

A correctly installed thinset bed is approximately the height of the collapsed trowel ridges, which is about half the notch size. 1/4 in square notch → 1/8 in bed. 3/8 in notch → 3/16 in bed. The ANSI A108 standard specifies a minimum 3/32 in bed for ceramic tile and 1/8 in for porcelain. Any thinner and the bond strength drops; any thicker and the thinset cures with too much water in it, losing strength. For large format (18 in and above) or heavy tiles (natural stone), the standard minimum is 3/16 in, which is why those formats step up to larger notches.

The thickness depends on purpose. A shower pan mud bed (deck mud) runs 3/4 in minimum at the drain, stepping up as slope increases toward the curb — average is about 1 to 1-1/2 in. A floor mud bed for raising or flattening a slab runs 1/2 in minimum and up to 3 in before you need to add wire mesh reinforcement. A mortar bed for setting natural stone tiles can go to 3–4 in if the substrate is particularly uneven. Anything over 3 in needs a reinforcing layer of 16 gauge wire mesh stapled to the substrate before you pack the mud.

Yes. Dry pack mortar for a shower pan is 4 volumes of clean sand to 1 volume of Type I or Type II Portland cement. The cement is the glue — the sand is the filler. Portland cement comes in 94 lb bags (1 cubic foot volume), which is convenient because one bag plus four shovels of sand makes exactly 5 cubic feet of dry pack. Do not use premixed concrete or prebagged deck mud for shower pans — those products contain gravel and are designed for structural fills, not for sloped shower pan compaction. Mapei 4-to-1 Mud Bed Mix, Sakrete Sand Mix, and Quikrete Sand Topping Mix are the brand equivalents.