Deck Mud Calculator
A deck mud calculator sizes shower pan mortar. A 3 × 5 ft pan with 1.25 in at the drain and 2.5 in at the walls needs 2.34 ft³, or 5 bags of 60 lb mix.
Deck mud calculator: bags for a shower pan
A deck mud calculator tells you how much dry-pack mortar a shower pan needs. Multiply the floor area by the average thickness. The average is the midpoint between the drain thickness and the wall thickness. A 3 × 5 ft pan at 1.25 in and 2.5 in needs 2.34 ft³, which is 5 bags of 60 lb sand and topping mix.
What deck mud is
Deck mud is a damp mix of sand and portland cement. You pack it by hand. It holds its shape, so the installer can shape it into a slope before it sets.
Picture a tray of damp sand. The tray is deep at the edge and shallow at the drain. To find how much sand fills it, you multiply the tray’s area by its average depth. That is the whole idea.
The deck mud formula
- Area = length × width, in feet.
- Average thickness = (drain thickness + wall thickness) ÷ 2, in inches.
- Volume in cubic feet = area × (average thickness ÷ 12).
- Bags = volume ÷ bag yield, rounded up to a whole bag.
- Site mix: sand and cement share the volume by their parts. A 4:1 mix is 4 parts sand to 1 part cement, so sand is 4/5 of the volume and cement is 1/5.
The default drain and wall thicknesses differ by 1.25 in. That matches a slope of 1/4 in per ft over a 5 ft run from the drain to the wall.
Worked examples
These match the calculator exactly.
Example 1: a 3 × 5 ft pan, default thicknesses, 60 lb bags.
- Area: 3 × 5 = 15 sq ft
- Average thickness: (1.25 + 2.5) ÷ 2 = 1.875 in
- Volume: 15 × (1.875 ÷ 12) = 2.34 ft³ (0.087 yd³)
- Bags: 2.34 ÷ 0.5 = 4.69, rounded up to 5 bags
- Site mix 4:1: sand 1.88 ft³, cement 0.47 ft³
- Site mix 5:1: sand 1.95 ft³, cement 0.39 ft³
Example 2: a 6 × 8 ft pan, 1.0 in at the drain, 2.0 in at the walls, 80 lb bags.
- Area: 6 × 8 = 48 sq ft
- Average thickness: (1.0 + 2.0) ÷ 2 = 1.5 in
- Volume: 48 × (1.5 ÷ 12) = 6.00 ft³ (0.22 yd³)
- Bags: 6.00 ÷ 0.66 = 9.09, rounded up to 10 bags
- Site mix 4:1: sand 4.80 ft³, cement 1.20 ft³
- Site mix 5:1: sand 5.00 ft³, cement 1.00 ft³
Bag yields
| Premix bag | Yield (ft³) | Source |
|---|---|---|
| 60 lb sand and topping mix | 0.50 | Quikrete data sheet No. 1103; Tractor Supply listing |
| 80 lb sand and topping mix | 0.66 | Quikrete data sheet No. 1103 |
Quikrete’s data sheet is the manufacturer figure. Tractor Supply lists the 60 lb bag at 0.5 cu ft too. The 80 lb figure came from the Quikrete data sheet excerpt; check the printed yield on your bag before you buy.
Site mix split
| Ratio | Sand share | Cement share | Split of example 1 (2.34 ft³) |
|---|---|---|---|
| 4:1 | 80% | 20% | 1.88 ft³ sand, 0.47 ft³ cement |
| 5:1 | 83.3% | 16.7% | 1.95 ft³ sand, 0.39 ft³ cement |
These are loose volumes. Damp sand packs tighter, so measure by volume in a bucket you trust, or weigh the cement.
How to measure
- Measure the pan’s inside length and width at the floor, not the tile surface.
- Set the drain height first. The mud at the drain is the thinnest point.
- Measure the mud depth at the wall at the top of the slope. This is the thickest point.
- Enter the two depths in inches. The calculator averages them for you.
Common mistakes
- Using the wall thickness for the whole floor. The floor is thinner than the wall, so the average is lower.
- Ordering by the wall depth. That overbuys mix and wastes bags.
- Mixing bag sizes in one estimate. A 60 lb bag and an 80 lb bag have different yields, so run the calculator once for each size.
- Adding too much water. Dry-pack mud should hold its shape when squeezed. Wet mud weakens and cracks.
- Forgetting a spare bag. Buy one extra for mixing losses and any patch work.
Related calculators
Tile sets on top of the pan, so the tile shower cost calculator prices the wall tile. Set the tile with the thinset calculator, and use the mortar calculator for block and brick work.
Frequently asked questions
What is deck mud?
Deck mud is a stiff, damp mix of sand and portland cement that you pack by hand instead of pouring. Installers use it to build the sloped pan under a shower floor, or a floor under tile, because it holds its shape and can be shaped to a slope before it sets.
How thick should deck mud be for a shower pan?
The pan is thinnest at the drain and thickest at the walls. A common setup is about 1.25 in at the drain and 2.5 in at the walls, which matches a 1/4 in per ft slope over a 5 ft run. This calculator uses the midpoint of those two thicknesses as the average depth.
How many bags of deck mud do I need for a 3 by 5 foot shower?
A 3 × 5 ft pan at the default thicknesses holds 2.34 ft³ of mix. A 60 lb sand and topping bag yields 0.5 ft³, so you need 5 bags. An 80 lb bag yields 0.66 ft³, so you need 4 bags.
Can I mix deck mud from sand and cement instead of buying bags?
Yes. A 4:1 site mix uses 4 parts sand to 1 part portland cement, so 80% of the volume is sand and 20% is cement. For a 3 × 5 ft pan that is 1.88 ft³ of sand and 0.47 ft³ of cement. A 5:1 mix uses 1.95 ft³ of sand and 0.39 ft³ of cement.
How do I know the bag yield is right?
Read the yield printed on your bag, because products differ. Quikrete's data sheet for its sand and topping mix lists about 0.5 ft³ for the 60 lb bag and 0.66 ft³ for the 80 lb bag. One retailer lists 0.45 ft³ for the 60 lb bag, so use the lower figure if you want extra margin.
Estimates only. Verify quantities with your supplier before purchasing.