Grout precisely.
Pounds of grout for any tile installation. Accounts for tile size, joint width, and thickness so you buy the right bags.
How we calculated this
The grout needed per square foot depends on three tile characteristics: how much joint perimeter exists around each tile (smaller tiles = more joints = more grout), how wide the joints are, and how thick the tiles are (thicker tiles = deeper joints to fill). The calculator uses the industry standard formula from cement grout manufacturers like Mapei and Custom Building Products.
Small tiles (4×4, 6×6) need significantly more grout than large tiles at the same joint width, a mosaic or small subway tile installation can require 3-4x the grout of a 24×24 floor installation of equivalent area, because there are many more linear feet of joint per square foot of coverage.
Joint width is the other major driver. Modern rectified tiles allow 1/16" joints, which use about half the grout of standard 1/8" joints. Rustic installations with 1/4" or wider joints use substantially more. Match the joint width to the tile: using a narrow joint on unrectified tile creates uneven lines.
Sanded grout is required for joints wider than 1/8". The sand prevents the grout from shrinking and cracking in wider joints. Unsanded grout is for joints 1/8" and narrower, especially on polished stone or soft tile that sanded grout would scratch.
The 15% waste factor covers the small amount that sticks to the mixing bucket, float, sponge, and tile surfaces during cleanup. For large complex installations with lots of cuts or multiple sessions, bump to 20%. Always mix grout in complete bag quantities: partial bags don't color-match reliably when mixed in different batches.
Grout volume is joint length times joint size
Grout quantity has almost nothing to do with how much tile you bought and everything to do with how many joints that tile creates. A hundred square feet of 24 by 24 porcelain has about 100 linear feet of joint. The same hundred square feet in 2 by 2 mosaic has roughly 1,200. That is why one takes under two pounds of grout and the other takes ten, and why a coverage chart printed on a bag is useless until you know your tile size, joint width, and tile thickness.
The calculator above works out all three and returns pounds. This page covers the choice the calculator cannot make for you: sanded or unsanded, cement or epoxy, whether to seal and when, plus the drying timeline, grout haze, and the places caulk belongs instead of grout.
How we calculated these numbers▾
Coverage figures follow manufacturer published charts for cementitious grout, which vary by a few percent between brands; the calculator applies typical values and rounds to whole bags. Cementitious grout is specified to ANSI A118.6 and A118.7, epoxy grout to ANSI A118.3. Joint width guidance and movement joint requirements follow the TCNA Handbook, including EJ171, which governs where grout must stop and a flexible sealant must take over.
Sanded vs unsanded grout
Sanded grout contains fine aggregate. Unsanded does not. The rule is that joints one eighth of an inch and wider take sanded, and joints narrower than an eighth take unsanded, and both halves of that rule exist for a physical reason. Cement shrinks as it cures, and in a wide joint pure cement paste shrinks enough to crack; the sand is there to resist it. In a narrow joint the sand simply will not pack in, leaving voids, and on polished marble or glass the aggregate scratches the tile face as you work it.
A few practical extensions. Rectified porcelain set at a 1/16 inch joint takes unsanded. Standard 12 by 12 at 1/8 inch takes sanded. Polished stone at any width takes unsanded, or an epoxy formulated for stone, because the scratching risk outweighs the shrinkage risk. And if a joint width lands right at 1/8, sanded is the safer choice for anything but soft or polished surfaces.
Cementitious | Epoxy | Single-component | |
|---|---|---|---|
| Cost per bag or unit | $15-30 | $60-120 | $40-80 |
| Sealing needed | Yes, annually | Never | Never |
| Stain resistance | Moderate, porous | Excellent | Very good |
| Working time | Forgiving, 30 min | Short, 45 min pot life | Long, stays workable |
| Difficulty | Beginner friendly | Demanding, sticky | Easy but slow curing |
| Best for | Most floors and walls | Showers, kitchens, commercial | Small jobs, DIY showers |
The three grout families and where each belongs. Cementitious covers most residential work; epoxy earns its cost in specific places.
On epoxy grout for a shower, which is the pairing people ask about most: it is genuinely the better material there. It does not absorb water, never needs sealing, and resists the soap and mineral staining that turns cement grout grey within a couple of years. The cost is real and so is the difficulty. Epoxy is sticky, it sets on a fixed clock regardless of how far along you are, and haze left behind hardens into something that has to be ground off. For a first-time DIY shower, a single-component grout is the compromise worth knowing about: most of the stain resistance, none of the pot life panic.
Sealing: what it does and does not do
Cementitious grout is porous, so a penetrating tile grout sealer soaks in and makes the surface repel water and oil for a while. It buys time to wipe a spill before it stains. It does not make grout waterproof, it does not prevent cracking, and it wears off, which is why the usual recommendation is to reseal every year or two in wet areas. Epoxy and single-component grouts need no sealer at all, and applying one to them accomplishes nothing.
Two products get confused here. A penetrating sealer is invisible and soaks in. A colour sealer, sold as grout color sealing or a grout sealer colorant, is a pigmented coating that sits on the surface, changes the colour, and effectively refinishes discoloured grout without regrouting. The second is a legitimate way to rescue stained grout, but it is a coating: it can peel if applied over dirty or damp joints, and it needs the joints genuinely clean first.
Drying time, haze, and the sponge
Cementitious grout is firm enough for light foot traffic at about 24 hours and cured enough to seal or to get wet at 72. Those figures stretch in a cold or humid room and shrink in a warm dry one. Work the grout in diagonally across the joints with a rubber grout float held at about 45 degrees, then strike off the excess with the float on edge. The instruction that matters more than either: do not flood fresh grout with water to clean it. Excess water pulls cement to the surface, weakens the joint, and produces blotchy colour that cannot be fixed afterward. A barely damp sponge, wrung until it stops dripping, is the correct tool.
Grout haze is the thin cement film left on the tile face, and it is normal rather than a mistake. Wiped at the right moment, 30 to 60 minutes after grouting when the joints have firmed but the haze is still soft, it comes off with a damp sponge and then a dry cloth. Left overnight it needs a haze remover, which is a mild acid, and left for a week on porous or polished stone it can etch. The window is the whole game.
Where grout stops and caulk begins
Every change of plane gets flexible sealant, not grout. That means inside corners where two walls meet, the joint where walls meet the floor or shower pan, around tub and shower bases, and where tile meets a different material. The TCNA calls these movement joints and covers them in EJ171. The reason is simple: those junctions move as the building expands, contracts, and settles, and rigid cement grout in a moving joint cracks every time.
Grout manufacturers sell colour-matched sealant, often sold as grout caulk, for exactly this, which is why a shower has grout on the field and caulk in the corners in the same colour. The most common repair call in tiled showers is cracked grout in a vertical corner, and the correct fix is never more grout. It is raking out the failed joint and running the matching sealant.
A 60 by 32 inch shower: 82 square feet of 3 by 6 subway on the walls at 1/16 inch joints, and 13 square feet of 2 by 2 mosaic on the floor at 1/8 inch.
The walls at a 1/16 joint need unsanded grout, roughly 1.6 pounds, so one 10 pound bag covers it several times over. The floor mosaic at 1/8 needs sanded, about 1.3 pounds despite being a sixth of the area, because the joint count is enormous. Two different grouts, two small quantities, and the practical decision is whether to run epoxy on both for a Nashville bathroom that sees daily use. Epoxy adds about $90 over cementitious across this shower and removes annual sealing forever, which is the trade most people take once they see the numbers side by side. Corners and the pan junction get colour-matched sealant either way.
Composite illustration based on typical project dimensions, regional contractor pricing, and 2026 material costs. Not a specific real project.
Where grout jobs go wrong
Too much water. Covered above and worth repeating because it is the single most common cause of weak, patchy, and crumbling grout. Wring the sponge until it barely dampens your palm.
Grout in the corners. Rigid grout in a moving joint cracks. Corners, plane changes, and perimeters take sealant.
Sealing too early. Sealer applied at 24 hours traps moisture inside a joint that has not finished curing, which can cause discolouration and a hazy film. Wait the full 72 hours.
Mixing bags separately. Grout colour varies slightly between bags and between mixes with different water content. On a large floor, mix consistently, keep the water measured rather than eyeballed, and where possible use bags from the same lot.
The rest of the tile job
Grout is the last step of a longer sequence. Tile quantities come from the tile calculator, a shower splits into walls and floor through the shower tile calculator, and a kitchen run belongs to the backsplash calculator. If the substrate is going in at the same time, the drywall calculator covers backer board.
Enter your tile size, joint width, and thickness above, buy one bag more than the number says, and keep the leftover sealed for repairs. Matching grout years later is harder than matching tile.
Frequently asked
How many bags of grout do I need?
For a typical 10×12 ft floor with 12×12 tiles and 1/8" joints, you need about 2-3 standard 25-lb bags. Small tiles or wider joints need more. The calculator above gives you the exact pound and bag count for your specific installation.
Should I use sanded or unsanded grout?
Sanded: joints 1/8" or wider, all floor installations. Unsanded: joints narrower than 1/8", polished marble or other soft stone, glass tile. If you're unsure, 1/8" is the breakpoint, at exactly 1/8", either works but sanded is more common.
How long does grout take to dry?
Cement grout is walk-on ready in 24-48 hours but takes 7 days to fully cure. Don't seal, scrub, or wet-clean for at least 72 hours. Epoxy grout cures faster (24 hours) but is harder to work with and more expensive.
Do I need to seal grout?
Cement grout: yes: apply a penetrating sealer 48-72 hours after installation, then reapply every 1-3 years. This prevents stains and water penetration. Epoxy grout: no: it's already non-porous. Premium pre-mixed grouts (like TEC AccuColor) often have sealer built in.
Can I reduce grout use with wider tiles?
Yes: 12×24 or 24×24 tiles use much less grout per square foot than 4×4 or 6×6 because there's less total joint perimeter. Large tiles also show dirt in grout lines less, require less cleaning, and install faster. The tradeoff is subfloor flatness: larger tiles are less forgiving of uneven floors.
What if my tiles have different thicknesses?
Use the thickest tile's dimension for grout calculation: grout fills to the top of the thickest tile. For installations mixing thicknesses, use back-buttering or thicker thinset under thinner tiles to level the surface; grout doesn't fix large thickness differences.
How accurate is the coverage formula?
The formula is within 5-10% for standard installations. Real-world variability: some grout gets wasted in the bucket, some joints end up slightly wider than planned, some tiles absorb grout in their beveled edges. The 15% waste factor covers typical variance; add more for complex patterns or large cuts.
Can I mix different grout colors?
Don't mix colors in the same joint: they'll blotch. For different rooms or feature walls, use distinct colors but mix each separately with its own water-to-powder ratio. For color consistency, always mix full bags at a time and note the batch number when buying multiple bags.
Sources
- ANSI A118.6 and A118.7: Cementitious Grouts - The standards covering standard and high performance cement grout
- ANSI A118.3: Chemical Resistant Epoxy Grout - The specification epoxy grouts are tested against
- TCNA Handbook EJ171: Movement Joints - Where grout must stop and a flexible sealant is required instead
- Mapei: Grout Coverage Charts - Published coverage by tile size, joint width, and tile thickness
- Custom Building Products: Grout Selection and Coverage - Sanded and unsanded selection guidance and per-bag coverage data
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