Published August 17, 2026 · Updated August 23, 2026 · By Tupep
You cannot compare them by the pound
Cement grout comes in 10 and 25 pound bags and the coverage chart is in pounds per square foot. Epoxy grout comes in kits with a resin, a hardener, and a filler, sold by the unit, and the unit weight is not comparable because epoxy is less dense than cured cement grout. Convert one to the other by weight and you will buy the wrong amount.
The fix is to stop thinking in pounds and calculate the thing that is actually fixed: the volume of the joints. Joint volume does not care what you fill it with. Once you have cubic inches, you can convert to either product with one multiplication.
The two step formula
Step 1. Joint volume per square foot (cubic inches) = 144 x T x J x (L + W) / (L x W)
Step 2a. Cement grout pounds = volume x 0.0725
Step 2b. Epoxy grout pounds = volume x 0.060
L and W are tile length and width in inches, T is tile thickness, J is joint width. The two constants are the approximate densities of the cured products in pounds per cubic inch. Epoxy densities vary by brand, so check the data sheet, but 0.060 is a workable planning figure.
Worked example: a shower with two tile sizes
Walls are 90 square feet of 3×6 ceramic, 5/16 inch thick, 1/16 inch joints. The pan is 14 square feet of 2×2 porcelain mosaic, 1/4 inch thick, 1/8 inch joints.
- Wall joint volume: 144 x 0.3125 x 0.0625 x (9/18) = 144 x 0.3125 = 45; 45 x 0.0625 = 2.8125; x 0.5 = 1.406 cu in per sq ft. Times 90 = 126.6 cu in.
- Pan joint volume: 144 x 0.25 x 0.125 x (4/4) = 144 x 0.25 = 36; 36 x 0.125 = 4.5 cu in per sq ft. Times 14 = 63.0 cu in.
- Total joint volume: 126.6 + 63.0 = 189.6 cu in.
- Waste allowance, 20 percent because epoxy is stickier and more of it stays in the pail: 189.6 x 1.20 = 227.5 cu in.
- If cement: 227.5 x 0.0725 = 16.5 lb, so one 25 lb bag.
- If epoxy: 227.5 x 0.060 = 13.7 lb. Most epoxy units run around 10 to 11 pounds, so two units.
Notice the mosaic pan. It is 13 percent of the tiled area and it is one third of the grout. When a job mixes tile sizes, run each one separately or you will be short.
Joint volume by tile and joint
These are cubic inches per square foot. Multiply by your area, add your waste factor, then convert.
| Tile | Thickness | 1/16 in joint | 1/8 in joint | 3/16 in joint |
|---|---|---|---|---|
| 1×1 mosaic | 1/4 in | 4.50 | 9.00 | 13.50 |
| 2×2 mosaic | 1/4 in | 2.25 | 4.50 | 6.75 |
| 3×6 subway | 5/16 in | 1.41 | 2.81 | 4.22 |
| 12×12 | 3/8 in | 0.56 | 1.13 | 1.69 |
| 12×24 | 3/8 in | 0.42 | 0.84 | 1.27 |
| 24×48 | 3/8 in | 0.21 | 0.42 | 0.63 |
What you are actually buying with epoxy
| Cement grout | Epoxy grout | |
|---|---|---|
| Sold as | 10 or 25 lb bags, dry powder | Kits, resin plus hardener plus filler |
| Density used for planning | 0.0725 lb per cu in | About 0.060 lb per cu in |
| Working time | Commonly 30 to 45 minutes | Commonly 45 to 60 minutes, temperature sensitive |
| Cleanup window | Sponge over 15 to 30 minutes | Wash within minutes, in two passes |
| Sealing | Commonly recommended in wet areas | Not required, it is not porous |
| Stain resistance | Absorbs, especially light colors | Very high |
| Joint range | 1/16 to 1/2 in depending on type | Usually 1/16 in and wider, check the sheet |
| Cost | Low | Several times higher per square foot |
Where each one belongs
We spend the money on epoxy in three places: kitchen backsplashes behind a range, shower pans and any horizontal wet surface, and anywhere the grout is light colored and the traffic is heavy. It does not absorb, so it does not go grey along the traffic path, and it does not need to be resealed on a schedule nobody keeps.
Cement grout is the right call almost everywhere else. On a large floor with wide joints, the epoxy cost gets serious fast, and cement grout with a good sealer performs fine. Cement is also far more forgiving of a slow crew.
The things that go wrong with epoxy
- Mix full units only. Many brands prohibit splitting a kit, because the resin to hardener ratio has to be exact. If you cannot place a full unit inside its pot life, you need a second person, not a smaller batch.
- Temperature drives everything. Below roughly 60 degrees F epoxy thickens and will not wash off cleanly. Above about 85 F the pot life shortens sharply. Bring the material to room temperature the night before and work in the shade.
- Two pass washing is mandatory. An open water wash with a scrubby pad to emulsify the residue, immediately followed by a clean water pass with a squeegee or a fresh sponge. Skip the second pass and you get a haze that will not come off with water once it cures. Removing cured epoxy haze means a chemical stripper and a lot of regret.
- Test on porous or textured tile. Unglazed quarry tile, tumbled stone, crackle glaze and heavily textured porcelain will hold epoxy in the surface. Grout one spare tile and let it cure before you commit to the room.
- Epoxy is not a movement joint either. Perimeter and change of plane joints still get a flexible sealant. Use the manufacturer’s matching sealant so the color lines up.
One last planning note. Because epoxy comes in fixed units and you cannot open a partial kit next weekend, we always round up to the next whole unit rather than trying to hit the number exactly. Running short of epoxy mid shower is not a trip to the store, it is a cold joint in the middle of a wall.
Related guides
- Grout for Large Format Tile
- Sanded vs Unsanded: Joint Width Decides, Not Preference
- How Much Grout for a Subway Tile Backsplash
- Large Format Tile: Why 10% Waste Is Not Enough
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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