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Demand {{ resultsReady ? formatArea(computation.values.demand_area_m2) : '—' }} Coverage {{ resultsReady ? formatCoverage(computation.values.coverage_per_bag_m2) : '—' }} Contact target {{ resultsReady ? `${installationProfile.requiredCoverage}%` : '—' }}
Tile Ridges {{ installationProfile.requiredCoverage }}% Skim
Presets are estimating starts, not product specifications.
Choose the measurement you already have before openings and mortar allowances.
Changing the unit preserves the physical area.
Value
Changing the shared unit converts both displayed dimensions without changing the physical surface.
Length
Changing the shared unit preserves the physical wall surface.
Wall run
Must be smaller than the measured surface. Its unit is independent of the surface input.
Area
Dry areas use an 80% contact target; wet and exterior areas use 95%.
This selector updates the trowel and skim/back-butter starting assumptions.
Coverage varies with the product, substrate, tile back, trowel angle, and installation practice.
The selected basis is scaled to the actual bag weight below.
Coverage
{{ formatPercent(waste_percent) }}
Applied to net tile area before the skim/back-butter allowance.
%
{{ formatPercent(back_butter_percent) }}
Use a product- and tile-specific allowance; the calculator does not verify achieved contact.
%
Confirm both bag weight and coverage on the selected mortar data sheet.
Weight
Use zero unless unopened repair stock or batch matching is part of the purchase plan.
Optional material-only subtotal in USD.
$
Bag takeoff
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Calculation method:
All values come from the canonical takeoff model; presentation only changes units and rounding.
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The chart renderer is unavailable. The selected bag takeoff and installation checks remain available.
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A mortar takeoff begins with the surface that will actually receive tile, then asks how much of that surface one bag can cover. The area may come from a measured rectangle, a wall run and tile height, or an already known total. Openings are removed before allowances are added.

Published bag coverage is an estimating yield, not a promise. Trowel notch, trowel angle, substrate flatness, mortar consistency, tile-back texture, and installation technique all change how far a bag goes. Large or deeply textured tile may also need mortar worked onto the back, which consumes material beyond the combed bed.

FactorEffect on the estimateWhat to verify
Untiled openingsReduce net tile areaSubtract only surfaces that will receive no mortar
WasteAdds material for cuts, setup loss, and irregular workMatch the allowance to the layout and job conditions
Skim or back-butteringAdds a second demand allowance after wasteInspect tile backs and follow the mortar and tile guidance
Bag weight and label yieldSet coverage per purchased bagUse the exact product label rather than a generic trowel estimate

Whole bags must cover the calculated demand, so a fractional answer rounds upward before any optional spare bags are added. That protects the purchase quantity from being rounded down, but it does not prove that the installed mortar achieved enough contact.

Mortar contact is a workmanship and safety check. The installation guidance used here calls for at least 80% contact in dry areas and 95% in wet or exterior areas, with tile edges supported. Lift tiles during the work to check ridge collapse and coverage; a bag count alone cannot detect voids, unsuitable mortar, missing movement joints, or a poor substrate.

How to Use This Tool:

Start from measurements and product information you can verify, using presets only as estimating starts.

  1. Choose Known tile area, Floor or wall rectangle, or Wall run × height, then enter the measured surface and any opening that receives no tile.
  2. Select the Installation exposure and Tile format. These choices set contact guidance and starting checks; they do not replace the installation specification.
  3. Choose a Trowel coverage profile. Prefer Custom product-label coverage when the selected mortar publishes a yield for the planned notch, then confirm the actual bag weight.
  4. Enter waste and skim or back-butter allowances. Add sealed spare bags only when repair stock or batch matching is part of the purchase plan.
  5. Read Bags to buy with Coverage per selected bag and the installation checks. Correct any invalid opening or zero dimension before relying on the takeoff.

Interpreting Results:

Exact bags is the unrounded material ratio. Bags to buy rounds that value up to a whole bag and then adds the requested spares. Surplus coverage is the estimated yield left after that purchase; it is not guaranteed leftover mortar.

The trowel comparison shows how a different generic coverage assumption changes the takeoff. Treat it as a sensitivity check, not permission to choose a notch by bag count. The mortar data sheet, tile size and back pattern, substrate, and required contact govern the installation.

A material subtotal covers bags only and stays in US dollars. It omits tax, delivery, tools, substrate preparation, waterproofing, labor, and unused-product return rules.

Technical Details:

All surface measurements are normalized to square metres and all bag weights to kilograms. Unit changes preserve the physical quantity. Waste is applied to net tile area first; the skim or back-butter allowance is then applied to the area after waste.

Formula Core

Let Ag be gross surface area, Ao excluded opening area, w the waste percentage, and b the skim or back-butter percentage. Mortar demand area is:

Ad=(Ag−Ao)×(1+w100)×(1+b100)

A coverage value stated for a 50 lb bag is scaled to the entered bag mass M. The exact conversion used is 50 lb = 22.6796185 kg.

Cbag=C50×M22.6796185

Whole-bag rounding happens before optional spares S are added:

Nbuy=⌈AdCbag⌉+S

A verified 12 ft by 15 ft large-format floor is 16.7225472 m². With 12% waste, 15% back-buttering, and 4.1806368 m² coverage per 50 lb bag, demand is 21.5386407936 m² and the exact result is 5.152 bags. The purchase quantity is 6 bags.

Lookup Core

Generic trowel profiles use these estimating yields for a 50 lb bag. A product-specific value should replace them when available.

Trowel profileft² per 50 lbm² per 22.6796185 kg
3/16 in V-notch958.8257888
1/4 × 1/4 in square notch827.61804928
1/4 × 3/8 in square notch635.85289152
1/2 × 1/2 in square notch454.1806368
3/4 in heavy-bed profile252.322576

Rule Core

Opening area must be strictly smaller than gross area. Waste accepts 0% through 50%, skim or back-buttering accepts 0% through 40%, and bag count always rounds upward. Dry floor and dry wall profiles use an 80% contact target; shower, wet-area, and exterior profiles use 95%. The back-butter check compares the entered allowance with the larger starting value from the tile format and exposure selections.

References: