How many tiles do I need?
Divide the floor area by the area of one tile, then add waste for cuts. Straight lay wastes about 10%. Diagonal, herringbone and large-format layouts usually want 15–20%, because nearly every perimeter tile gets cut.
Measure in rectangles, then buy by the box
Measure the room as a set of rectangles rather than one length and one width. Take each measurement at floor level with a tape, not off a plan. Walls are rarely square, and drywall mud and baseboard can swallow the inch you were counting on. Add the doorway thresholds, the alcove, and the strip behind the toilet and under the vanity if you’re tiling beneath them. Then add the rectangles together.
Multiplying the longest length by the widest width is the classic mistake. On an L-shaped room it overbuys badly, and around a kitchen island or a peninsula it quietly underbuys, which is far worse. Sketch it, measure each block, and total them.
You can’t buy 143 tiles. Tile is sold by the carton, and cartons are sized in square feet rather than pieces. A 12 x 24 in porcelain typically ships eight tiles to a box covering about 15.5 square feet, while 12 x 12 boxes commonly hold 15 to 17 square feet. Convert your waste-adjusted area to whole boxes and round up from there rather than from tile counts.
On a small bathroom that round-up alone can add another five to ten percent on top of your cutting allowance. That’s fine. It becomes the spare box you’ll probably be glad of in five years.
Order the whole job in one delivery and check the shade and caliber codes printed on every carton before you open them. ANSI A137.1 grades tile for shade variation from V1 (pieces from a run are near-identical) through V2 and V3 up to V4, where color and texture differ substantially from tile to tile by design. With V3 and V4 you have to open four or five boxes at once and pull from all of them as you lay. Otherwise the floor develops visible patches that no amount of grout will disguise. V1 carries a different risk. Two production runs of the same uniform tile can still sit subtly apart.
Choosing the tile: absorption, wear and slip
What separates porcelain from ceramic? A lab test, whatever the showroom says. Under ANSI A137.1 (tested to ASTM C373), porcelain is defined as tile with a water absorption of 0.5 percent or less. That density lets it go into wet rooms, onto unheated porches and anywhere it might freeze. It’s also why porcelain cuts harder and needs a decent continuous-rim diamond blade. Ordinary glazed ceramic absorbs more, costs less and is perfectly good on walls and light-traffic floors indoors. It isn’t the material for a shower floor, an exterior threshold or a porch step.
Wear resistance on a glazed tile is graded by its PEI abrasion class, from ASTM C1027. Class 0 and I are wall tiles and very light residential use. Class II suits light residential floors away from entrances. Class III covers most residential floors, kitchens and hallways included, and classes IV and V handle heavy residential and commercial traffic. For a family kitchen, a hall, or anywhere grit gets tracked in from outside, PEI III is usually the sensible minimum. A through-body porcelain also keeps looking right longer than a glaze once wear does start to show, since the color runs all the way through.
Slip resistance has a number too, and it’s worth asking for. ANSI A137.1 requires a wet dynamic coefficient of friction of 0.42 or greater, measured to ANSI A326.3, for tile marketed for level interior floors expected to be walked on wet (bathrooms, entryways, kitchens and mechanical rooms). The figure appears on the manufacturer’s spec sheet.
A polished tile that doesn’t meet 0.42 is a wall tile or a dry-room tile, whatever the display says. Choosing a smaller format or tighter grout joints doesn’t change the reading.
Where the calculator's assumptions run out
The thin-set figure follows the notch, and the notch follows the tile size. Here that means about 95 square feet a bag behind a 1/4 inch notch. Manufacturers’ coverage tables typically run around 90 to 100 square feet a bag with a 1/4 x 1/4 in square notch, roughly 60 with a 1/4 x 3/8, and only 40-odd with a 1/2 x 1/2. So a large-format floor that needs the bigger notch takes roughly twice the mortar shown here, and it pays to read the table on the actual bag.
Add more again on an uneven floor, because the mortar is making up the difference. And remember the standards call for mortar contact over 80 percent of the tile back in dry areas, and 95 percent in wet areas and outdoors.
Layout has hard limits too. For any tile with a side longer than 15 inches, the maximum offset in a running bond is 33 percent unless the manufacturer states otherwise. A 50 percent brick bond puts the crowned middle of one tile against the low edge of its neighbor, and the lippage that produces can’t be grouted out. Substrate tolerance tightens at the same threshold. ANSI A108.02 allows 1/4 inch in 10 feet under tiles with all edges shorter than 15 inches, but only 1/8 inch in 10 feet once any edge reaches 15. Deflection limits are L/360 for ceramic and L/720 for natural stone.
Finally, the calculator counts tiles, mortar and grout. It doesn’t count movement joints, and those aren’t optional. TCNA method EJ171 (TTMAC detail 301MJ in Canada) calls for a soft joint every 20 to 25 feet in each direction on interior floors, tightening to every 8 to 12 feet outdoors or anywhere in direct sunlight. It also wants a quarter-inch gap wherever the tile meets a wall, column, threshold or a change of substrate. Fill those with a compressible backer strip and a flexible sealant, never with grout.
A perimeter grouted solid to the wall is the usual reason a floor tents a year later. Check your local code or supplier if you’re unsure where the joints should go.
Deck mud calculator, for a mortar bed · Self-leveling calculator, for a floor that is out of flat
How much thinset for 100 sq ft of tile
Two 50 pound bags for most floors. Custom’s VersaBond data sheet rates a 1/4 by 1/4 inch square notch at 90 to 100 square feet per bag, and a 1/4 by 3/8 inch notch at 60 to 67. So 100 square feet takes 1 to 1.7 bags, depending on which trowel the tile calls for. Large format on a 1/2 inch notch takes three.
The notch decides the coverage, and the tile decides the notch. Anything with an edge 15 inches or longer is large format by the ANSI definition. It wants a 1/2 by 1/2 inch square notch or a slant U-notch, where coverage drops to 42 to 47 square feet a bag on Custom’s own sheet. Other brands publish 30 to 50 for the same trowel (Mapei 40 to 50, Laticrete nearer 35), so treat it as a range and read your own bag.
Back-buttering costs another 15 to 20 percent. Large format usually needs it to hit the ANSI A108.5 contact minimum of 80 percent in dry areas and 95 in wet ones. Mix 6 quarts of water per 50 pound bag, and expect about four hours of working life in the bucket.
How much grout for 12x12 tile
You’ll probably need less than you think. Custom’s Polyblend Plus sanded grout chart puts one 25 pound bag at 348 square feet of 12 by 12 by 3/8 inch tile with a 1/8 inch joint, 234 square feet at 3/16 inch, and 177 at 1/4 inch. One bag usually covers a typical kitchen floor outright.
Joint width matters more than area. Doubling the joint roughly halves what a bag does, because you’re filling a bigger void around the same tile. Tile size pulls the same lever from the other end. At a 1/8 inch joint that 25 pound bag drops to 138 square feet on 3 by 3 tile and 54 on 1 by 1 mosaic, since small formats pack far more joint into every square foot.
The calculator carries a deliberately safe 120 square feet per bag, because it has to cover mosaics and subway too. On 12 by 12 with a normal joint you’ll be comfortably inside it. Buy one bag and mix it in one batch so the color is identical wall to wall.
How much extra tile should I buy for waste
Start at 10 percent over your measured area for a straight lay in a square room. Go to 15 percent for diagonal, 15 to 20 for herringbone, and 20 percent where there are many cuts and obstacles. Those are the usual industry baselines. Then round up to whole boxes and keep whatever’s left over as attic stock.
Percentages break down on small rooms. Ten percent of a 40 square foot bathroom is 4 square feet (four 12 by 12 tiles), which one bad cut and one dropped box corner will eat before lunch. Under about 100 square feet, ignore the percentage and add a full box instead. Keep the offcuts too. You’ll want them for practicing the awkward cuts.
The surplus isn’t really waste. Tile runs get discontinued constantly, and a cracked tile five years from now is either a spare from your own box or a visible patch in a different shade.
How many tiles in a box
There’s no fixed number. Cartons are packed to a one-person lift of roughly 45 to 65 pounds and labeled in square feet rather than pieces. A 12 by 24 inch carton typically holds 7 to 9 tiles covering 13.5 to 17.6 square feet. A 12 by 12 carton runs anywhere from 11 to 17 tiles, or about 11 to 15.5 square feet.
Take three real examples off the shelf. A Lifeproof 12 by 24 porcelain ships 8 pieces at 15.6 square feet and 64.7 pounds, a Style Selections 12 by 24 ships 7 at 13.58, and a Daltile Volume carton of the same nominal size covers 17.6. Same tile size, three different box counts.
The pieces don’t divide evenly because nominal isn’t actual. A 12 by 24 is usually 300 by 600 millimeters, which is 11.81 by 23.62 inches, or 1.94 square feet rather than 2.
Order against the square footage printed on the carton, and let the piece count fall out of it however it does.
Common questions
How much waste should I add for tile?
For a straight lay in a square room, add ten percent. Diagonal wants fifteen, herringbone fifteen to twenty, and a complex room with lots of obstacles is usually a twenty percent job.
How much thin-set and grout?
Figure on roughly one 50 lb bag of thin-set per 85–95 sq ft with a 1/4 in square notch. Once large-format tile puts you on a 1/2 in notch and you’re back-buttering, it’s only about 40 sq ft a bag. Grout is one 25 lb bag per 120 sq ft with typical joints, and it goes much further than that on 12 x 12 and larger.
Do large tiles need a flatter floor?
Yes. Any tile with an edge 15 in or longer needs the substrate flat to 1/8 in in 10 ft. Anything looser and the corners stand proud as lippage.
How many 12x24 tiles do I need for 100 square feet?
Each 12 x 24 tile is 2 square feet, so 100 square feet plus 10 percent for a straight lay is 110 square feet, or 55 tiles. Boxes of eight cover about 15.5 square feet, so you’re really buying 8 boxes (124 square feet and 64 tiles). Treat the surplus as your spare box rather than waste.
How many boxes of tile do I need?
Take your measured area, add the waste percentage for your layout, then divide by the square footage printed on the carton. Round up to whole boxes, not to whole tiles. Coverage per box varies by size and thickness, so check the actual carton. A 12 x 24 box is usually about 15.5 square feet, and a 12 x 12 box 15 to 17.
What size trowel do I need for 12x24 tile?
Large-format tile normally wants a 1/2 x 1/2 in square notch or a slanted U-notch, plus back-buttering to reach the required mortar contact. That drops coverage to roughly 40 to 50 square feet per 50 lb bag (about half what a quarter-inch notch achieves), so double the mortar allowance before you place the order.
Can I lay 12x24 tile in a 50 percent brick pattern?
Not safely. Any tile with a side longer than 15 inches should be offset by no more than 33 percent. At half offset the natural crown along a long tile lines up against the low edge of the next one and shows as lippage. A third offset lands each joint over the flatter middle of the tile below.
Is porcelain or ceramic better for a bathroom floor?
Porcelain, in almost every case. By definition it absorbs 0.5 percent water or less, so it copes with a wet floor and with freezing in an unheated room. Also check that the wet DCOF is 0.42 or higher (the ANSI threshold for level interior floors expected to be walked on wet), and aim for PEI III.
How many 12x12 tiles do I need for 100 square feet?
Nominal sizes trip people up here. A nominal 12 by 12 is usually 11.81 inches actual, or 0.97 square feet, so 100 square feet takes about 104 tiles. Add 10 percent for a straight lay and you’re at 114, which is 8 to 10 cartons. Cases of 12 by 12 range from around 11 square feet up to 15.5, so check the label rather than assuming.
Do I use sanded or unsanded grout for 12x12 tile?
Sanded, in almost every case. Custom rates its sanded grout for joints from 1/8 inch up to 1/2, which is where 12 by 12 floor tile normally lands. Unsanded covers the 1/16 to 1/8 inch range, plus polished stone or glass that sand would scratch, so the two overlap at 1/8 rather than dividing cleanly there. They have different coverage rates, so don’t carry a sanded chart across to an unsanded bag.
How much does a box of tile weigh?
Plan on about 45 to 65 pounds for standard floor formats. A Lifeproof 12 by 24 carton is 64.7 pounds, a Style Selections 12 by 24 is 57.4, and an American Olean Abound 12 by 12 carton is 48.7. Boxes are sized around a one-person carry rather than a tile count. Ten boxes is roughly 600 pounds, which usually means a trailer or two trips rather than a car trunk.