What this mortar bed estimate measures
A flat mortar bed has volume equal to its area multiplied by its thickness. Because the area is in square feet and thickness is in inches, divide the thickness by 12 before finding cubic feet.
Divide the adjusted volume by the mixed-volume yield of one bag. Bag weight alone does not establish that yield; use product information or a verified trial for the actual mix and package.
Flat, constant-thickness volume estimate only. Enter confirmed mixed-volume yield for one exact bag. The prefilled 0.45 cu ft per bag is illustrative, not a product yield; versions can differ. This does not design a sloped shower bed, choose a mix or verify permitted thickness.
How to use this calculator
- Project area. Enter the measured area of the flat bed in square feet. Separate sections with different thicknesses into separate estimates.
- Specified constant thickness. Enter the already specified constant thickness in inches. This calculator does not determine an allowable thickness or a slope.
- Confirmed mixed yield per bag. Enter the confirmed mixed-volume yield in cubic feet for one complete bag of your exact product. Do not enter the dry bag weight or use a yield from a different mix version.
- Waste / allowance. Optionally add an explicit percentage to geometric volume once. Empty or zero adds no allowance.
Select Calculate to update the result. Reset restores the example inputs and recalculates the example estimate.
Formulas, variables, and units
netVolumeCuFt = areaSqFt × thicknessIn / 12
- areaSqFt
- Flat measured area in square feet.
- thicknessIn / 12
- Constant thickness converted from inches to feet.
- netVolumeCuFt
- Geometric bed volume in cubic feet.
adjustedVolumeCuFt = netVolumeCuFt × (1 + wasteRate / 100)
- wasteRate
- Optional explicit percentage applied to volume.
- adjustedVolumeCuFt
- Volume basis including that allowance.
requiredBags = adjustedVolumeCuFt / yieldCuFtPerBag; bags = ceil(requiredBags); purchasedVolumeCuFt = bags × yieldCuFtPerBag
- yieldCuFtPerBag
- Confirmed mixed-volume yield of one exact bag, in cubic feet.
- requiredBags, bags
- Fractional requirement and whole-bag purchase, respectively.
- purchasedVolumeCuFt
- Nominal mixed volume represented by the whole bags.
How to read your result
Net volume is geometry before an additional allowance. Adjusted volume includes that allowance once.
Bag demand remains unrounded until the final purchase count. Purchased volume is nominal product yield, not usable surplus or a guarantee of finished thickness.
Displayed values use up to two decimal places. Complete purchase units are rounded upward from the unrounded requirement.
A worked purchase example
- Project area
- 12 sq ft
- Specified constant thickness
- 1.5 in
- Confirmed mixed yield per bag
- 0.45 cu ft / bag
- Waste / allowance
- 10 %
- A hypothetical flat 12 ft² bed at 1.5 in has 12 × 1.5 / 12 = 1.5 ft³ geometric volume.
- An elected 10% allowance gives 1.5 × 1.10 = 1.65 ft³.
- With a hypothetical confirmed yield of 0.45 ft³ per bag, 1.65 / 0.45 = 3.6666666667 bags.
- Round upward to 4 bags, representing 4 × 0.45 = 1.8 ft³ nominal mixed volume.
Independent geometry and division. The 0.45 ft³ input is illustrative, not a named product preset. The example establishes neither thickness suitability nor a sloped-bed design.
Frequently asked questions
Can I calculate a sloped shower floor?
This model uses one constant thickness. It does not model slopes, drain position or variable thickness and does not design shower assemblies.
Can I convert bag pounds directly to cubic feet?
No universal conversion is supplied. Mixed yield depends on the exact product and preparation; enter the confirmed cubic feet yielded by the actual bag.
Is the prefilled bag yield a product specification?
No. The 0.45 cu ft per bag belongs to the adjustable arithmetic example. Captured product records can differ by version; replace it with confirmed mixed yield for the exact product and package.
Is nominal purchased volume usable excess?
Not necessarily. It represents complete bags at the stated yield; mixing, placement and other losses can change actual volume.
Scope and limitations
Project types
- Flat constant-thickness tile setting bed
Check the calculator assumptions and product conditions for your project.
Calculation limits
- Flat, constant-thickness volume estimate only. Enter confirmed mixed-volume yield for one exact bag. The prefilled 0.45 cu ft per bag is illustrative, not a product yield; versions can differ. This does not design a sloped shower bed, choose a mix or verify permitted thickness.
- No slope, drain design, mix proportion, structural or assembly compliance calculation.