Published August 13, 2026 · Updated August 23, 2026 · By Tupep
This is not a style choice
People pick sanded or unsanded grout the way they pick a paint sheen. It is not that kind of decision. The two products fail in opposite directions, and which one fails is decided almost entirely by how wide your grout joint is.
The working rule most manufacturers publish: unsanded for joints from 1/16 up to 1/8 inch, sanded for 1/8 inch and wider. At exactly 1/8 either will usually work, and on a floor we go sanded. Outside that band, using the wrong one does not look slightly worse. It comes apart.
Why each one fails
Unsanded grout is cement, pigment, and polymer with no aggregate, and cement paste shrinks as it cures. In a 1/16 inch joint there is so little material that the shrinkage is invisible. Put that paste in a 1/4 inch joint and the shrinkage pulls the grout off the tile edges and cracks it, usually a week or two after the job looks finished. Sand does not shrink, so it holds a wide joint stable.
Sanded grout in a narrow joint fails the other way. The sand grade will not pass into a 1/16 inch gap. The grains bridge across the opening near the surface and underneath them is air. The joint looks full on grouting day and starts hollowing out the first time somebody scrubs it. On a shower wall that void is a path for water.
A third category is worth knowing. Single component and high performance grouts use a finely graded aggregate plus polymers and are commonly rated from 1/16 to 1/2 inch out of one bag. On a job with mixed joint widths that is usually the cleanest answer.
| Joint width | Use | What happens with the wrong choice |
|---|---|---|
| 1/32 to 1/16 in | Unsanded only | Sanded bridges and leaves voids under the surface |
| 1/16 to 1/8 in | Unsanded, or high performance | Sanded may pack but leaves a rough, pitted joint |
| 1/8 in exactly | Either works | Judgment call, go sanded on floors |
| 1/8 to 1/2 in | Sanded, or high performance | Unsanded shrinks, cracks and pulls off the tile edge |
| Over 1/2 in | Sanded, packed in lifts | Single pass leaves a hollow core |
What decides your joint width in the first place
Most people get the order of operations backwards. You do not pick a joint width because you like the look. The tile picks it, and then the tile picks the grout.
Rectified tile has been mechanically ground to a precise size after firing, so every piece is the same to within a hair. That is what allows a 1/16 inch joint. Cushioned edge tile, which is most pressed ceramic and a lot of porcelain, comes out of the kiln with a slightly rounded edge and real variation from piece to piece. Try to hold a 1/16 inch joint on cushioned edge tile and the variation shows up as joints that wander from tight to open across the same run.
The guidance commonly given in the industry is that the grout joint should be at least three times the actual variation in facial dimension of the tile, with 1/16 inch as a practical floor even for rectified. So if your 12×24 varies by 1/32 inch piece to piece, the minimum joint is 3/32, and in practice you would run 1/8 or 3/16. Check the tile manufacturer’s stated minimum joint width, because on many large format lines a joint tighter than what they specify voids the warranty.
The volume difference, worked out
Joint width is a linear term in the grout volume formula, so tripling the joint triples the grout. Same tile, same floor, wildly different orders.
Pounds per square foot = 10.4 x T x J x (L + W) / (L x W)
Take an 80 square foot bathroom floor in 12×24 porcelain, 3/8 inch thick. The shape term is (12 + 24) / (12 x 24) = 36 / 288 = 0.125.
- At 1/16 inch, unsanded: 10.4 x 0.375 x 0.0625 x 0.125 = 0.0305 lb per sq ft. 80 x 0.0305 = 2.44 lb. Plus 20 percent = 2.9 lb.
- At 1/8 inch, either: 10.4 x 0.375 x 0.125 x 0.125 = 0.0609 lb per sq ft. 80 x 0.0609 = 4.88 lb. Plus 20 percent = 5.9 lb.
- At 3/16 inch, sanded: 10.4 x 0.375 x 0.1875 x 0.125 = 0.0914 lb per sq ft. 80 x 0.0914 = 7.31 lb. Plus 20 percent = 8.8 lb.
Three times the joint, three times the grout, on an identical floor. The 1/16 job leaves most of a 10 pound bag. The 3/16 job nearly empties one, and we would buy 25 pounds so the floor comes out of one lot.
| Joint | Grout type | lb per sq ft | 80 sq ft floor | Bag to buy |
|---|---|---|---|---|
| 1/16 in | Unsanded | 0.0305 | 2.9 lb | One 10 lb |
| 1/8 in | Sanded or unsanded | 0.0609 | 5.9 lb | One 10 lb |
| 3/16 in | Sanded | 0.0914 | 8.8 lb | One 25 lb |
| 1/4 in | Sanded | 0.1219 | 11.7 lb | One 25 lb |
Practical notes from the float
- Test sanded grout on a spare tile if the tile is polished marble, mirrored glass, or a high gloss porcelain. Run the float across it hard, wash it, and look at it in raking light. Some tiles are fine and some scratch on the first pass.
- Wide joints get two passes. On tile thicker than about 1/2 inch with a 3/8 inch joint, pack, strike, and pack again. A single pass leaves a void in the middle that you cannot see.
- Sanded grout needs a harder float and more pressure. Working it like unsanded leaves the joints underfilled at the tile edges.
- Do not add water on the cleanup pass. A sopping sponge pulls cement out of the joint and leaves the sand behind, which is what creates that pale, gritty, mottled look people blame on the color.
Related guides
- Epoxy Grout Coverage vs Cement Grout
- Grout for Large Format Tile
- How Much Grout for a Subway Tile Backsplash
- Subway Tile Backsplash: How Many Square Feet for a Kitchen
Sources and Further Reading
Run your own numbers with the Grout Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
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