Thinset & Mortar Calculator
Setting details
Bigger tile needs a bigger notch.
Required for most tile 15 in and larger.
Thinset needed
2 bags
- Coverage per 50 lb bag
- 75 sq ft
- Area to set
- 120 sq ft
- Back-butter allowance
- None
- Effective area
- 120 sq ft
Buy one extra bag — partial bags absorb moisture and go off quickly once opened.
Do this math on the job site — in the free app
Smart Tile Calculator for Android: offline, in your pocket, no ads. iPhone version coming soon.
Tools the pros use for this job
Notched Trowel
Goldblatt 1/2'' x 1/2'' x 1/2'' Square-Notch Tile Trowel, 11'' x 4.5'' | Stainless Steel Blade, Soft Grip Handle, Square Notch Design for XLarge Ceramic Tile Floor, Pavers, EIFS
Check price on AmazonMatch notch depth to tile size — this is the #1 coverage variable.
Mixing Paddle
Edward Tools Paint and Mud Mixer for Drill - Mixes 1 to 3 Gallons - 15 3/4" Length - 5/16" Hex Shaft - Zinc Plated Steel - Reinforced Weld - Non Slip Hex Head - Easy Clean - Paint Mixer Attachment
Check price on AmazonLump-free mortar in two minutes; hand mixing never gets there.
Modified Thinset
Sponsored Ad - 3 Pack 12x24 Inch Heavy Duty Grout Mortar Bags with Tip-Blue | Heavy Duty PVC Tear Resistant Puncture Tip Cement Sealer Bag, Grout Bag for Tile Installation, Easy to clean
Check price on AmazonPolymer-modified mortar for porcelain and large-format tile.
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How this calculator works
Coverage figures assume a 50 lb bag, a clean flat substrate, and correct trowel technique — combed in one direction, tile pressed and slid perpendicular to the ridges to collapse them.
- Mosaic and small tile: 3/16" V-notch
- Up to 12": 1/4" × 1/4" square notch
- 12"–16": 1/4" × 3/8"
- Large format 18"+: 1/2" × 1/2" plus back-buttering
Back-buttering large tile adds roughly 30–40% more mortar but is required to hit the 95% coverage that warranties and wet areas demand.
Frequently asked questions
How many bags of thinset for 100 square feet?
With a 1/4 x 3/8 inch notched trowel, about 75 sq ft per 50 lb bag — so two bags for 100 sq ft. Large-format tile with a 1/2 inch notch needs three.
Do I need modified or unmodified thinset?
Use polymer-modified for porcelain and most floors. Use unmodified when setting over an uncoupling membrane or when the membrane manufacturer specifies it — check the membrane instructions first.
Can I use extra thinset to level a floor?
No. Thinset is an adhesive, not a leveler. Fix dips with a self-leveling underlayment or patch compound before tiling, or the tile will crack.
Related calculators
- Tile Quantity CalculatorHow many tiles you need for any room, wall, or floor — with waste.
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- Shower Tile CalculatorWalls, floor, curb, and niche for a full shower surround.
- Tile Cost EstimatorTotal project cost: tile, grout, mortar, trim, and labor.
Guides worth reading next
- Modified vs Unmodified Thinset: The 30-Second Answer (and the Long One)Which mortar for porcelain, which for Kerdi and Ditra, what ANSI A118.4 and A118.1 ratings mean, and why the bag price difference is worth it.
- How to Measure a Room for Tile (Step by Step)Measure any room for floor or wall tile: handle closets and alcoves, convert inches to decimals, subtract fixtures, and add the right waste percentage.
- Choosing the Right Tile Size for Your RoomHow tile size changes a room: when 12×24 beats 4×4, why small rooms can take large tile, grout line math, and the flatness rule for big formats.