Flooring & Tile
Grout Calculator
Enter the tiled area, the tile length, width and thickness, and the joint width. We fill the joints on paper and tell you the pounds of grout and the bags to buy.
Worked example
- Joint share of each tile = (12 + 12) x 0.125 / (12 x 12) = 2.08% of the area.
- Volume = 100 sq ft x 0.0208 x 0.375 in / 12, plus 10% = 0.072 cu ft.
- At about 105 lb per cu ft: 7.5 lb.
Common sizes at a glance
| Size | Grout | 25 lb bags |
|---|---|---|
| 3 x 6 in, 1/16 in joint, 100 sq ft | 11.3 lb | 1 |
| 6 x 6 in, 1/8 in joint, 100 sq ft | 15 lb | 1 |
| 12 x 12 in, 1/8 in joint, 100 sq ft | 7.5 lb | 1 |
| 12 x 24 in, 1/8 in joint, 100 sq ft | 5.6 lb | 1 |
| 24 x 24 in, 3/16 in joint, 100 sq ft | 5.6 lb | 1 |
Four things set the amount of grout
- Joint width: a 3/16 in joint holds half again as much as a 1/8 in joint.
- Tile thickness: the joint is as deep as the tile, so thick tile takes more.
- Tile size: smaller tile means more joints in every square foot.
- Area: the total square footage being grouted.
Small tile, big grout order
Joint share is the part of the surface that is grout, not tile. In the example, 12 x 12 in tile with a 1/8 in joint leaves 2.08% of the floor as joint, and 100 sq ft needs about 7.5 lb.
Switch to a 3 x 6 in tile with a 1/16 in joint and the same 100 sq ft needs about 11.3 lb, even though the joint is half as wide. Mosaics and subway tile are where grout estimates most often come up short.
Sanded or unsanded
The joint width usually decides the type. Unsanded grout is made for very thin joints, and sanded grout is the usual choice once the joint reaches about 1/8 in, because the sand helps wider joints resist shrinking and cracking.
Read the bag for the joint range it allows. The calculator gives weight for a standard cement grout; other grout types list their own coverage, so follow the label if it differs.
Buying and mixing tips
Grout is sold in bags by weight. Buy all of it at once from the same lot so the color matches, and keep a little for touch-ups.
Mix only what you can finish before it starts to stiffen. A big batch that sets up in the bucket is grout you will have to buy again.
Where grout fits in the job
Grout is the last material to go on. Count tiles first with the tile calculator, then the setting mortar with the thinset calculator, and finish with this page.
Questions
How much grout do I need for 100 sq ft of 12 x 12 tile?
With a 1/8 in joint and 3/8 in thick tile, about 7.5 lb. One 25 lb bag covers that with room to spare.
Why does a backsplash need so much grout?
Backsplash tile is often small, so a square foot has many more joints. Enter the real tile size and the calculator accounts for it.
What waste allowance should I use?
About 10% covers grout left on the float, in the bucket and wiped off the face. Raise it if you are new to grouting.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.