Measure Your Coverage Area
Multiply length by width in feet to get square feet. A 10 × 10 ft floor is 100 sq ft. Split an L-shaped area into rectangles and add them together, then enter the total under “I know my area.”
Measure walls and floors separately, subtracting surfaces that will not receive tile. Run a separate estimate when they need different trowels or mortars. Use the tile calculator for tile quantities; this tool estimates the mortar beneath those tiles.
Trowel Size and Mortar Coverage
Tile size is a starting point for trowel selection. MAPEI’s guidance pairs smaller tiles with smaller notches and larger tiles with deeper notches; the tile back and substrate also matter. Check the bedding by lifting a freshly placed tile and following your product’s instructions.
| Trowel | Typical tile size | sq ft / 50 lb bag |
|---|---|---|
| 3/16″ V-notch | Mesh mosaics, 3 × 6 and smaller | 3/16 in V-notch: about 90–100 sq ft per 50 lb bag (installation-guide figures; manufacturers don't publish a TDS value for this notch). |
| 1/4″ × 1/4″ | Up to 8 × 8 (MAPEI) | 75–100 |
| 1/4″ × 3/8″ | 10 × 10–17 × 17 | 55–80; over DITRA 40–50, DITRA-XL 35–45 |
| 1/2″ × 1/2″ | 18 × 18–12 × 36 (including 12 × 24) | 35–50 |
| 3/4″ U-notch | 24 × 24 and larger, slabs | 34–47 (MAPEI does not publish this tier) |
The technical data sheet (TDS) for the specific product you buy takes priority over this table.
The lower endpoint is used for Bags to buy (the conservative estimate); the upper endpoint is used for If you trowel tight. Figures reference manufacturer data sheets including LATICRETE 253 GOLD DS-296 and Custom VersaBond TDS-119. These ranges assume a flat substrate, a trowel held at about 45° and full bedding.
Compare the Tile Shop installation coverage chart, Schluter’s DITRA coverage FAQ and MAPEI’s trowel-size guidance. Manufacturer TDS ranges vary by product, including Kerabond T / Keralastic and Ultraflex LFT. Lightweight mortars can cover more per pound; use their stated coverage per bag instead of converting from 50 lb.
How much mortar has to touch the tile. ANSI A108.5 requires an average contact area of at least 80%, except on exterior or shower installations, where it is 95%. Those figures only count if the coverage is “sufficiently distributed to give full support of the tile” — a strong average with one hollow corner still fails the standard.
Natural stone is stricter. The TCNA Handbook requires 95% in both dry and wet areas, with no voids larger than 2 square inches and no voids within 2 in of the tile corners, and every corner and edge fully supported.
Sources: CTEF on back-buttering and ANSI/TCNA contact requirements and CTEF on trowel notches and mortar coverage.
How Many Bags Do You Need
For Bags to buy, divide your area, including extra allowance, by the lower coverage number. For If you trowel tight, use the higher coverage number. Both round up to whole bags; the two numbers can be the same on a small project. A custom coverage value gives one buying estimate instead of a range.
MAPEI recommends 5–10% extra in its material estimates; this tool starts at 0% because the lower coverage endpoint is already conservative. Buy whole bags and keep unopened spares dry. Open bags can absorb moisture and become unusable.
Optional cost is the Bags to buy count multiplied by your price per bag. It excludes tile, grout, preparation, labor, delivery and tax. Use the grout calculator to estimate the material for the joints separately.
Back-buttering is not part of this number. Coating the back of a tile increases bond strength and fills in the back pattern, but the TCNA Handbook states that it “does not constitute coverage.” There is no published percentage to add for it, which is why this calculator doesn’t add one.
If you plan to back-butter, have extra mortar ready: use your product’s TDS coverage row or enter a 5–10% allowance.
Thinset vs Medium-Bed Mortar
Thinset mortar bonds tile in a thin setting bed. “Medium-bed” is an older label often used for mortars intended for larger or heavier tiles; current bags may say large-and-heavy-tile or LFT mortar. Choose a product approved for your tile, substrate and required bed thickness.
Mortar type does not change this calculation. The selected trowel and substrate set the coverage range; your product’s TDS coverage can replace it. This estimate does not include leveling or patching the substrate.
Worked Example: 100 Square Feet
A 10 × 10 ft floor with 12 × 24 inch tile, a 1/2″ × 1/2″ trowel and a standard substrate uses the 35–50 sq ft range per 50 lb bag.
- Area: 10 × 10 = 100 sq ft.
- Extra allowance: 0%, so the estimated area stays at 100 sq ft.
- Bags to buy: 100 ÷ 35 = 2.86, rounded up to 3 bags.
- If you trowel tight: 100 ÷ 50 = 2, giving 2 bags.
Coverage figures are estimates for one 50 lb (22.7 kg) bag and assume a flat substrate, a trowel held at about 45°, and full bedding. Actual coverage varies with mortar consistency, substrate flatness, trowel angle, tile thickness and back-buttering — the manufacturer's technical data sheet for your specific product always wins. Ranges come from manufacturer data sheets (MAPEI, Custom Building Products VersaBond, Laticrete) and Schluter's DITRA/DITRA-XL coverage FAQ; the 3/16 in V-notch figure comes from installation guides such as The Tile Shop's coverage chart, because manufacturers don't publish one. Buy at least one spare bag and keep the receipt. Tiling Lab is not affiliated with these companies.