Key takeaways
- Grout joints change the count, so tiles per sq ft = 144 ÷ ((length + joint) × (width + joint)).
- Waste advice ranges from 5% to 25% depending on layout, and none of it comes from a primary standard.
- Thin-set coverage depends on the trowel notch, so use your product's chart.
Enter the area and your tile's actual size, including the joint you plan to use. Choose the notch your mortar's chart lists for the job.
How the calculator works
- Tiles per square foot: 144 ÷ ((length + joint) × (width + joint))
- Tiles to buy: area × (1 + waste %) × tiles per square foot, rounded up
- Grout volume: area × tiles per square foot × depth × joint × (length + width + joint)
- Thin-set bags: area ÷ low end of the chart's coverage, rounded up
These are our own geometry, so check the result against your product's chart.
Worked example
100 square feet of 12 × 12 inch tile, with a 1/8-inch joint, 3/8 inch deep, and 10% waste:
- Tiles per square foot: 144 ÷ (12.125 × 12.125) = 0.98
- Tiles to buy: 100 × 1.10 × 0.98 = 107.7, so 108 tiles
- Grout: about 111 cubic inches
- Thin-set at a 1/4-inch square notch: 100 ÷ 85 = 1.2, so 2 bags
How waste changes with layout
We found no primary published figure. Consumer guides vary, so these are rules of thumb:
| Layout | Advice we found |
|---|---|
| Straight lay, large tile | 5–7% |
| Straight lay, medium tile | 7–10% |
| Diagonal | 15–25% |
On our 100-square-foot example, that's about 103 tiles at 5%, 108 at 10% and 123 at 25%. Keep a few spare tiles for later repairs, because a later batch may not match.
Joints and offsets
The Ceramic Tile Education Foundation quotes the ANSI A108.02 standard as setting these figures. We read them through that article rather than the standard itself:
- Minimum average joint: 1/8 inch for rectified tile and 3/16 inch for calibrated tile, increased for edge warpage
- Offset patterns: at most 33% unless the tile maker says otherwise, where the offset side is over 15 inches
So a very thin joint or a 50% brick pattern isn't something to assume. Check your tile maker's instructions.
Mortar and grout
CUSTOM MultiSet's chart lists 85 to 95 square feet per 50 lb bag with a 1/4-inch square notch, and 60 to 67 with a 1/4 × 3/8-inch notch. It also calls for at least 80% contact in dry areas and 95% in wet areas and exteriors. Larger tile can need a larger notch, and other products differ.
We show grout as volume because we didn't find a reliable density to turn it into pounds. Your grout's coverage chart is the right place for that.
Wet areas
For tile on tub and shower walls, 2021 IRC Table R702.4.2 lists backer types including glass mat gypsum, fiber-reinforced gypsum, non-asbestos fiber-cement and cementitious units. Check what your local code has adopted.
Before you remove the old floor
Old floors and adhesive can contain asbestos. Read about old flooring before you sand, scrape or pull anything up.
Frequently asked questions
Do grout lines change how many tiles I need?
Yes, slightly, and more with small tiles. Each tile plus its joint takes up a larger area than the tile alone.
How much extra tile should I buy?
There's no single standard. Guides range from about 5% for simple straight lays to 25% for some diagonals.
Why don't you give grout in pounds?
We'd need a product's density, and we didn't find one we could trust across brands. Your grout's chart gives pounds for its own product.
Sources
We use primary sources where we can: building codes, federal rules and manufacturer documents. Read our editorial standards.
- CUSTOM Building Products: MultiSet mortar
- 2021 International Residential Code, Chapter 7, Table R702.4.2
- Ceramic Tile Education Foundation: Offsets and grout joints
- Flooring Clarity: How much extra tile (a rule of thumb, not a standard)