Deck Mud Calculator
A 30 square foot bed at a uniform 1.25-inch thickness has 3.125 cubic feet of volume before extra waste. With the calculator's 5-to-1 assumptions, that rounds to 7 bags of 50 lb sand and 1 full 94 lb bag of Portland cement. Enter area, average thickness, ratio, sand bag weight, and waste to estimate materials. The model treats finished mud volume as equal to sand volume. Cement volume is sand volume divided by the entered ratio. It assumes dry sand at 100 lb per cubic foot and Portland cement at 94 lb per cubic foot. These are planning densities and a mortar-yield convention. Moisture, sand grading, compaction, slope, substrate variation, and product packaging can change actual yield.
Quick answer
Deck mud volume is area times thickness, converted to cubic feet.
What this tells you
- •Deck mud volume is area times thickness, converted to cubic feet.
- •Standard deck mud is 5 parts sand to 1 part Portland cement by volume.
- •Finished mud volume is treated as the sand volume, because cement and water fill the gaps between sand grains.
- •Bag counts round up so you do not run short mid-pour.
- •Waste multiplies the full bed volume before sand and cement quantities are calculated.
- •The ratio means parts sand per 1 part cement by volume, not by bag count.
- •Material weights round to whole pounds, while bag counts always round upward.
- •Sloped beds need an average thickness or geometry that captures the slope.
How to Use
- 1Enter the floor or pan area in square feet.
- 2Enter the finished bed thickness in inches.
- 3Adjust the sand-to-cement ratio if your recipe differs from 5-to-1.
- 4Set your sand bag weight (50 lb is common).
- 5Optionally add a waste allowance, then calculate.
- 6Use average thickness for a uniformly sloped bed rather than only the drain or perimeter depth.
- 7Compare bag counts with the actual product weight and coverage printed by your supplier.
- 8Check the required mortar-bed assembly, membrane, reinforcement, and minimum thickness.
How It Works
Formula
Mud Volume (cu ft) = Area x Thickness(ft)
Sand Volume = Mud Volume x (1 + waste)
Cement Volume = Sand Volume / Ratio
Sand Bags = ceil(Sand Volume x 100 / Bag Weight)
Cement Bags = ceil(Cement Volume x 94 / 94)The calculator converts thickness to feet, computes bed volume, applies any waste allowance, then splits the mix by the sand-to-cement ratio. Sand is estimated at 100 lb per cubic foot and Portland cement at 94 lb per cubic foot (one bag).
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Shower pan, 30 sq ft at 1.25 inches
Thirty times 1.25 / 12 equals 3.125 cu ft. The model uses 312.5 lb of sand, needing 7 fifty-pound bags. Cement is 3.125 / 5 x 94 = 58.75 lb, so 1 full bag is required.
Floor bed, 100 sq ft at 1.5 inches
The bed is 12.5 cu ft before waste. Applying 10% gives 13.75 cu ft, 1,375 lb of sand, and 2.75 cu ft or about 259 lb of cement. Bag counts round up to 28 and 3.
Small repair with 4-to-1 mix
The base volume is 1 cu ft and waste raises it to 1.10. That is 110 lb of sand, rounded up to 3 bags. Cement is 1.10 / 4 x 94, or about 26 lb, so a full bag is still required.
Changing the sand bag size
The sand estimate is 500 lb. Dividing by 60 gives 8.33, so the order rounds up to 9 bags. Cement is 1 cu ft, modeled as 94 lb or 1 standard bag.
Deck Mud per 100 Square Feet (5-to-1 Recipe)
Approximate sand and Portland cement for a 100 sq ft bed at common thicknesses, before waste.
| Thickness | Mud Volume | Sand (50 lb bags) | Cement (94 lb bags) |
|---|---|---|---|
| 1 in | 8.3 cu ft | 17 | 2 |
| 1.25 in | 10.4 cu ft | 21 | 3 |
| 1.5 in | 12.5 cu ft | 25 | 3 |
| 2 in | 16.7 cu ft | 34 | 4 |
Sand at 100 lb per cubic foot, cement at 94 lb per bag. Round up and mix a test batch first.
Mix yield, thickness, and jobsite planning
Deck mud, also called dry-pack or floor mud, is a stiff sand and Portland cement mortar used to build shower pans and level tile beds. The widely used recipe is 5 parts sand to 1 part Portland cement by volume, mixed with just enough water to hold a packed shape when squeezed.
Some installers run as lean as 6-to-1 or as rich as 4-to-1 depending on the sand. Richer mixes are easier to carve but can shrink, so 5-to-1 is the common middle ground. A minimum finished thickness of about 1.25 inches keeps the bed strong enough to resist cracking.
A shower pan is rarely one uniform thickness. If a flat plane slopes from a constant perimeter to a centered drain, an average of perimeter and drain thickness may approximate volume. Irregular footprints, off-center drains, benches, curbs, and multiple slopes need separate geometry or a measured allowance.
Bagged sand topping mix already contains cement and sand. The separate sand and Portland outputs should not be used as its bag count. Use calculated volume with the bag's published yield and follow product instructions.
Quantity is only one part of the assembly. Substrate preparation, cleavage membrane, waterproofing, reinforcement, bonding slurry, drain type, slope, movement joints, and cure conditions must match the chosen system and local requirements.
Common mistakes
- Entering thickness in feet instead of inches
- Using a bed thinner than about 1.25 inches
- Forgetting that bag counts are rounded up
- Mixing the mud too wet, which weakens the bed
- Using perimeter or drain thickness for the entire sloped area instead of an average
- Reading a 5-to-1 volume ratio as five bags of sand to one cement bag
- Assuming every sand product weighs exactly 100 lb per cubic foot
- Using separate-material outputs for a premixed sand topping product
- Ignoring substrate, waterproofing, slope, drainage, and curing requirements
Embed this calculator on your site
Drop this single line where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use with attribution.
<script src="https://calctide.com/embed.js" data-tool="deck-mud-calculator" async></script>Preview the embed at /embed/deck-mud-calculator/.