Floor Mud Calculator
Work out how many bags of pre-mixed floor mud to buy for a tile mortar bed or a sloped shower pan, from the area and the bed's average thickness. This page covers packed sand-and-cement mortar beds only; self-leveling underlayment is a different, pourable product and is not estimated here.
Area and bed thickness
Use the average depth from the finished height down to the floor, not the deepest spot.
Results
For a 8 ft × 5 ft mortar bed averaging 1 in thick, you'll need about 6 80 lb bags of floor mud.
Floor mud needed
6 bags (80 lb)
That's a typical amount for leveling a bathroom or kitchen floor.
Mix in batches you can pack and screed within the product's pot life instead of all at once, and set screed rails at the finished height before you start.
Bed area: 40 sq ft
Average bed thickness: 1 in
Mortar volume incl. 10% buffer: 3.67 cu ft
Yield per bag: 0.66 cu ft
How this works
To find how much floor mud you need, multiply the bed's area by its average thickness to get the mortar volume, add a 10% BuildyWork planning buffer, divide by the volume one bag yields, and round up to whole bags. A flat bed has one average thickness. A shower pan does not: the QUIKRETE sheet says floor mud in a shower must be sloped toward the drain at 0.25 in per foot, so the bed is thinnest at the drain and thickest at the walls. Find the area first with the square footage calculator.
| Product | Published yield per bag | Used here |
|---|---|---|
| QUIKRETE Floor Mud, 80 lb bag | Approximately 0.66 cu ft (18.7 L) | 0.66 cu ft |
| QUIKRETE Floor Mud, 60 lb bag | Approximately 0.50 cu ft (14 L) | 0.5 cu ft |
| LATICRETE 209 Floor Mud, 60 lb bag | Approximately 6 sq ft (0.56 m²) at 1" (25 mm) thickness | 0.5 cu ft |
Sources: QUIKRETE Floor Mud product data sheet (No. 1548-81) and LATICRETE 209 Floor Mud data sheet (DS-209-1026), checked 2026-10-30. LATICRETE publishes coverage at a 1 in thickness rather than a volume, which this calculator converts to 0.5 cu ft per bag. The thickness inputs accept 0.5 in to 2in, the range of beds the QUIKRETE sheet's admixture instructions describe; neither sheet states a separate minimum or maximum. The 10% buffer is a BuildyWork planning default with no external source claimed.
For a sloped shower pan with a center (point) drain and a level perimeter, the sloped surface is an inverted pyramid with its tip at the drain. A pyramid's volume is its base times its height divided by 3, so the average rise is 2/3 of the rise at the walls, wherever the drain sits. A linear drain along one wall makes a single sloped plane (a wedge), so the average rise is 1/2. The rise at the walls is the slope times the distance from the drain to the farthest wall. The calculator then adds a 10% BuildyWork planning buffer to the volume and divides by the bag yield. Bag yields come from the QUIKRETE Floor Mud product data sheet (No. 1548-81) and the LATICRETE 209 Floor Mud data sheet (DS-209-1026).
Worked example: leveling a bathroom floor
A 5 ft × 8 ft bathroom floor (40 sq ft) needs a mortar bed averaging 1 in thick under new stone tile. The mortar volume is 40 × 1/12 = 3.33 cu ft, and the 10% BuildyWork planning buffer brings it to 3.67 cu ft. With QUIKRETE Floor Mud 80 lb bags at about 0.66 cu ft each, that is 3.67 ÷ 0.66 ≈ 5.56, rounded up to 6 bags. With 60 lb bags at 0.50 cu ft, it is 3.67 ÷ 0.50 ≈ 7.33, rounded up to 8 bags.
A second example: a sloped shower pan with a center drain
A 3 ft × 5 ft shower has a center drain 2.5 ft from the farthest wall, and the bed is 1 in thick at the drain. At ¼ in per foot, the bed rises 0.25 × 2.5 = 0.625 in, so it is 1.625 in thick at that wall. The average thickness is 1 + 2/3 × 0.625 ≈ 1.42 in. The volume is 15 sq ft × 1.42/12 ≈ 1.77 cu ft, or 1.95 cu ft with the 10% buffer. That is 1.95 ÷ 0.66 ≈ 2.95, rounded up to 3 QUIKRETE 80 lb bags. Using the 1.625 in wall thickness for the whole pan would have given 3.39, or 4 bags.
Common mistakes
Using the wall thickness for the whole shower pan
A sloped pan is thickest at the walls and thinnest at the drain. Multiplying the whole area by the wall thickness overbuys; multiplying by the drain thickness underbuys. Use the sloped-pan setting so the average is worked out for you.
Using flat-bed math for a shower floor
Floor mud in a shower is sloped toward the drain, so the bed gets thicker with every foot of distance from the drain. Entering one thickness for a shower floor leaves that rise out of the estimate.
Measuring only the deepest spot when leveling a floor
One low spot does not set the thickness of the whole bed. Average several readings across the area, or split the area into zones with their own thickness.
Mixing more than you can place in time
LATICRETE 209 lists a pot life of 1 hour. Mix in batches you can pack and screed within that window rather than opening every bag at once.
Using self-leveler coverage figures for floor mud
A self-leveler's coverage per bag is published for a pourable product at a stated depth. It is not a floor mud yield, and using one in place of the other gives the wrong bag count.
When this calculator's model stops applying
- Beds thicker than 2 in: the QUIKRETE sheet describes beds from ½ to 2 in. For a deeper fill, check with the manufacturer before relying on this estimate.
- Two-layer shower pans: if your pan design has a separate sloped layer under the waterproof membrane as well as the mortar bed on top, run the calculator once for each layer.
- Non-rectangular showers and floors: enter the enclosing rectangle for a slight overestimate, or split the shape into rectangles and add the bag counts.
- A trench drain across the middle of the floor: the floor slopes to it from both sides. Choose the linear-drain setting and enter the larger of the two distances for a slightly high estimate.
- Curbs, benches and niches: their mortar is not part of the floor bed and is not included here.
- Site-mixed sand and portland cement: the bag counts use pre-blended bag yields, so they do not apply to a site mix (the mortar volume shown still does).
FAQ
Is floor mud the same thing as self-leveling underlayment?
No. Floor mud is a stiff, semi-dry sand-and-cement mortar that is packed, tamped and screeded by hand, which is why it can be sloped to a drain. Self-leveling underlayment is a pourable product sold by coverage at a stated depth. This calculator only estimates floor mud; for a self-leveler, use the coverage printed on that product's bag.
My drain is not in the middle of the shower. Does the center-drain setting still work?
Yes, as long as the perimeter is level and the floor slopes in flat planes from each wall down to the drain. Enter the distance from the drain to the farthest wall: that wall gets the slope you entered, and the closer walls end up steeper. The 2/3 average described under How this works holds for any drain position.
How do I find the average thickness of an uneven floor I want to level?
Set a level line or straightedge at the finished height, measure the depth down to the floor at several evenly spaced points, and average those readings. Using the deepest reading as the average overbuys; using the shallowest underbuys. If one area is much deeper than the rest, run that area separately.
Does an 80 lb bag go further than a 60 lb bag per pound?
Barely. By the published yields, QUIKRETE's 80 lb bag makes about 0.00825 cu ft per pound and its 60 lb bag about 0.00833 cu ft per pound, so cost per pound and how much you can lift decide the bag size more than yield does. LATICRETE 209's 60 lb bag works out to the same 0.5 cu ft as QUIKRETE's 60 lb bag.
Can I mix my own floor mud from sand and portland cement instead?
You can, but this calculator does not estimate a site mix. Its bag counts use the yields printed on pre-blended bags, and a site mix's yield depends on your own proportions and sand. The mortar volume the calculator shows is still the volume your bed needs, whichever way you make it.
Can I use floor mud outdoors?
It depends on the product. The QUIKRETE Floor Mud sheet lists exterior or interior use, while the LATICRETE 209 sheet says interior use only. The bag count is the same either way; the product choice is not.
Do I need lath, a bonding coat or an additive under the bed?
Often, and none of them change the bag count. The QUIKRETE sheet notes that ANSI requires lath over wood, calls for a fortifier in the mixing water for ½ to 1½ in beds and a bonding adhesive for 1 to 2 in beds. The LATICRETE 209 sheet calls for a slurry bond coat before the mortar is placed. Follow the sheet for the product you buy.
How much water goes into a bag of floor mud?
Follow the bag. The QUIKRETE sheet says about 4 quarts per 80 lb bag and no more than 5½ quarts in total; the LATICRETE 209 sheet lists about 0.7 gal per 60 lb bag and a stiff, semi-dry consistency. The yields this calculator uses are the ones the sheets publish for mortar mixed that way.
How soon can I tile over a floor mud bed?
Check your product's sheet, because the two differ. LATICRETE 209 lists a pot life of 1 hour, 12 hours to traffic and 72 hours to heavy traffic at 70°F. The QUIKRETE sheet says to let the initial set occur before spreading thin-set so the bed does not peel, and to keep curing for 5 days in warm weather.