Grout Calculator: How Much Grout Do I Need?

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100 sq ft of 12 x 12 in tile with 1/8 in joints takes about 6.5 lb of sanded grout, or 7.2 lb with 10% extra: one 25 lb bag, which covers about 384 sq ft.

How much grout do you need?

Enter the area to grout and your tile size. Type the tile thickness as a decimal (3/8 in = 0.375). We fill the joints to the tile's full depth and round up to whole bags.

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Pounds use MAPEI's grout formula (about 100 lb of dry grout per cubic foot of joint). Coverage differs by brand and between sanded and unsanded grout, so compare with the chart on your bag. Unsanded grout is made for joints up to 1/8 in; use sanded grout for wider joints.

Those figures assume 3/8 in thick tile and joints filled to full depth. Rule of thumb: double the joint width, or the tile thickness, and you double the grout.

Our grout calculator uses the consumption formula MAPEI publishes, converted to inches and pounds, and rounds up to whole bags.

How to measure for grout

Methods for taking the four measurements:

  1. Area to grout. Multiply length by width for a floor, or width by tiled height for a wall or backsplash. Split an L-shaped room into rectangles; our square footage calculator adds them up.
  2. Tile length and width. Read them from the box or measure a tile, in inches.
  3. Tile thickness. Measure it with a tape at a cut edge, or take it from the box, and type it as a decimal: 1/4 in = 0.25, 3/8 in = 0.375, 1/2 in = 0.5. It's used as the joint depth.
  4. Joint width. Read it from your spacers, from 1/16 to 1/2 in.

Then pick a 25 lb or 10 lb bag and the extra (10% to start).

The grout formula

MAPEI's data sheets give consumption in kg/m² as (A + B) ÷ (A × B) × C × D × 1.6, with tile length A, width B, thickness C, and joint width D in mm. In inches, with tile length L, width W, joint width J, and thickness T:

Pounds of grout per sq ft = (L + W) ÷ (L × W) × J × T × 8.32

  • (L + W) ÷ (L × W) × J is the joint share of the floor (joint length per square inch of tile × joint width): about 2% for 12 x 12 in tile with 1/8 in joints.
  • T fills the joints to the tile's full depth.
  • 8.32 comes from MAPEI's 1.6 kg of grout per liter of joint, about 100 lb per cubic foot (1.6 × 62.428 = 99.885). A square foot of joint 1 in deep holds 99.885 ÷ 12 = 8.32 lb. The calculator uses 8.3237.

Multiply by the area, add the extra, and round up to whole bags. MAPEI's form counts the square where joints cross twice, so it runs slightly high (1.6% for 12 x 12 in tile with 1/8 in joints), on the safe side. It reproduces every value in the full rows of MAPEI's 2024 Ultracolor Plus consumption table.

Worked example (the calculator's default values)

100 sq ft of 12 x 12 in tile, 0.375 in thick, 1/8 in joints, 25 lb bags, 10% extra:

  1. Joint share: 0.125 × 24 ÷ 144 = 0.020833
  2. Per sq ft: 0.020833 × 0.375 × 8.3237 = 0.06503 lb
  3. Grout: 100 × 0.06503 = 6.5 lb; with 10% extra, 7.15, shown as 7.2
  4. Bags: 7.15 ÷ 25 = 0.29, rounded up to 1
  5. Coverage: 25 ÷ 0.06503 = 384 sq ft per bag

The calculator shows: "You need about 7.2 lb of grout (1 bag of 25 lb)." and "100 sq ft of 12 x 12 in tile, 0.375 in thick, with 1/8 in joints filled to full depth: about 6.5 lb, plus 10% extra. One 25 lb bag covers about 384 sq ft with this tile and joint, before extra."

Second example: a subway tile backsplash

30 sq ft of 3 x 6 in tile, 1/4 in thick, with 1/8 in joints and a 10 lb bag: the joint share is 0.125 × 9 ÷ 18 = 0.0625, triple that of 12 x 12 tile, so each sq ft takes 0.0625 × 0.25 × 8.3237 = 0.1301 lb. That's 3.9 lb, or 4.3 lb with 10% extra, and one 10 lb bag covers about 77 sq ft. The calculator shows: "You need about 4.3 lb of grout (1 bag of 10 lb)."

With unsanded grout, check its chart: MAPEI's Keracolor U chart lists 104 sq ft per 10 lb for this tile and joint, so that product would need less.

Third example: several bags

250 sq ft of 6 x 6 in tile, 1/2 in thick, with 1/4 in joints: the joint share is 0.25 × 12 ÷ 36 = 0.08333, and each sq ft takes 0.08333 × 0.5 × 8.3237 = 0.3468 lb. That's 86.7 lb, or 95.4 lb with 10% extra, and 95.4 ÷ 25 = 3.8 rounds up to 4 bags. The calculator shows: "You need about 95.4 lb of grout (4 bags of 25 lb)." It puts one bag at about 72 sq ft; MAPEI's Keracolor S chart lists 71.

Grout for 100 square feet of 12 by 12 inch tile with 1/8 inch joints: 6.5 pounds, 7.2 with 10 percent extraLeft: top view of one 12 by 12 inch tile, length L by width W, with a joint J wide along its length and along its width, so each tile brings J times (L plus W) of joint for L times W of tile; the joint is drawn wider than scale. Right: section through a joint between two tiles: the joint J is 1/8 inch (0.125) wide and the grout fills it to the tile's full depth T, 3/8 inch (0.375). Pounds of grout per square foot equal (L plus W) divided by (L times W), times J, times T, times 8.32: (12 plus 12) divided by (12 times 12) times 0.125 is 0.020833 of the floor; times 0.375 and 8.3237 gives 0.06503 pounds per square foot. 100 square feet takes 6.5 pounds, or 7.15 with 10 percent extra, shown as 7.2: 1 bag of 25 pounds, which covers about 384 square feet.GROUT FOR 100 SQ FT OF 12 × 12 IN TILE1One tile and its jointsL × Wtile areaJ × WJ × LL = 12 inW12 inJoints drawn wider than scale2Section through a jointtiletileJ = 1/8 inT3/8 ingrout, filled to the full depth Tlb per sq ft = (L + W) ÷ (L × W) × J × T × 8.32Joint share: (12 + 12) ÷ (12 × 12) × 0.125 = 0.020833Per sq ft: 0.020833 × 0.375 × 8.3237 = 0.06503 lb100 sq ft × 0.06503 = 6.5 lb, + 10% extra = 7.15 → 7.2 lb1 bag of 25 lb; one bag covers 25 ÷ 0.06503 = 384 sq ft
Pounds per sq ft = (L + W) ÷ (L × W) × J × T × 8.32. For 12 x 12 in tile, 3/8 in thick, with 1/8 in joints: (12 + 12) ÷ (12 × 12) × 0.125 = 0.020833, × 0.375 × 8.3237 = 0.06503 lb per sq ft. 100 sq ft takes 6.5 lb, or 7.2 lb with 10% extra: one 25 lb bag, which covers about 384 sq ft.

Grout per 100 sq ft by tile size and joint width

Pounds per 100 sq ft, before extra, computed with the formula above:

Tile (in)1/16 in joint1/8 in3/16 in1/4 in3/8 in1/2 in
3 x 6, 1/4 thick6.513.019.526.039.052.0
4 1/4 x 4 1/4, 1/4 thick6.112.218.424.536.749.0
6 x 6, 1/4 thick4.38.713.017.326.034.7
12 x 12, 3/8 thick3.36.59.813.019.526.0
6 x 24, 3/8 thick4.18.112.216.324.432.5
12 x 24, 3/8 thick2.44.97.39.814.619.5
18 x 18, 3/8 thick2.24.36.58.713.017.3
24 x 24, 3/8 thick1.63.34.96.59.813.0

For 200 sq ft of 12 x 24 in tile with 1/8 in joints, that's 9.8 lb, or 10.7 lb with 10% extra: one 25 lb bag, which covers about 513 sq ft. Unsanded grout stops at 1/8 in. Many sanded grouts start at 1/8 in (Keracolor S, Polyblend Plus Sanded), but LATICRETE 1500 Sanded and Ultracolor Plus FA go down to 1/16 in.

Why the bag chart may differ

Coverage varies by product: MAPEI's calculator works from "the actual volume to be filled and the product density." Each maker's chart for 12 x 12 x 3/8 in tile with 1/8 in joints:

GroutMaker's chartThis calculator
MAPEI Keracolor S (sanded)383 sq ft per 25 lb384
MAPEI Ultracolor Plus FA388 sq ft per 25 lb384
CUSTOM Polyblend Plus Sanded348 sq ft per 25 lb384
MAPEI Keracolor U (unsanded)212 sq ft per 10 lb154 per 10 lb
CUSTOM Polyblend Plus Non-Sanded146 sq ft per 10 lb154 per 10 lb
  • Close match: for tile 6 in and up with joints to 1/4 in, the Keracolor S and Ultracolor Plus FA charts stay within 2% of the formula.
  • More grout: Polyblend Plus Sanded needs about 10% more than the calculator shows (384 ÷ 348).
  • Unsanded varies both ways: Polyblend Plus Non-Sanded needs about 5% more; Keracolor U about 27% less.
  • Mosaics: charts disagree even within one brand. For 1 x 1 in tile, the formula gives 9.6 sq ft per 25 lb at 5/8 in joints (Keracolor S chart: 7) and 8.0 at 3/4 in (Ultracolor Plus FA chart: 9).

Joints vary too: CUSTOM's coverage bulletin notes that 1/8 in joints off by 1/32 in change the grout needed by 25% (5/32 ÷ 1/8 = 1.25). These are makers' published numbers, not a ranking; compare this estimate with your bag's chart and plan on the larger amount.

Sanded or unsanded grout?

Choose by joint width first. Each maker's data sheet gives the range:

GroutTypeJoint widths
MAPEI Keracolor UUnsanded1/16 to 1/8 in
CUSTOM Polyblend Plus Non-SandedUnsandedUp to 1/8 in
MAPEI Keracolor SSanded1/8 to 5/8 in
CUSTOM Polyblend Plus SandedSanded1/8 to 1/2 in
LATICRETE 1500 SandedSanded1/16 to 1/2 in
MAPEI Ultracolor Plus FAFine aggregate1/16 to 3/4 in

MAPEI's Keracolor U sheet rules out joints wider than 1/8 in, and its Keracolor S sheet rules out joints under 1/8 in. LATICRETE advises unsanded grout for soft or polished marble, other soft stone, some polished stone, and soft glazed tile with joints of 1/8 in or less, and sanded grout for other tile and stone with joints from 1/16 to 1/2 in. The type doesn't change the calculator's math, only which chart to check.

Tips and common mistakes

  • Buy 5% to 10% extra. MAPEI recommends that much overage, since actual coverage may vary with job conditions and application methods.
  • Fill the joints. CUSTOM's tip is to fill joints at least 2/3 full; with epoxy or single-component grout, it lets the setting material fill the lower third. If you'll do that, enter two-thirds of the tile thickness (0.25 in for 3/8 in tile).
  • Check the joint you actually get. Measure a few joints once the tile is set; 1/32 in wider than 1/8 in takes 25% more grout.
  • Large tile. See the grout joints section of our tile calculator guide for joint-width rules.
  • Other grout types. For epoxy, urethane, or premixed grout, go by that product's coverage chart.

Frequently asked questions

How much grout do I need?

Multiply the area by (L + W) ÷ (L × W) × J × T × 8.32, all in inches, add 5% to 10%, and round up to whole bags. 100 sq ft of 12 x 12 x 3/8 in tile with 1/8 in joints takes about 6.5 lb, or 7.2 lb with 10% extra.

How much grout do I need for 100 sq ft?

With 1/8 in joints, about 6.5 lb for 12 x 12 in or 3.3 lb for 24 x 24 in tile 3/8 in thick, and 13.0 lb for 3 x 6 in tile 1/4 in thick, before extra. Double the joint to 1/4 in and each amount doubles.

How many square feet does a 25 lb bag of grout cover?

By the formula, about 384 sq ft of 12 x 12 x 3/8 in tile or 513 sq ft of 12 x 24 x 3/8 in tile with 1/8 in joints, but 72 sq ft of 6 x 6 x 1/2 in tile with 1/4 in joints. Makers' sanded and fine-aggregate charts for the 12 x 12 case run from 348 to 388 sq ft, so check your bag.

Sanded or unsanded grout: which do I need?

Go by joint width. The unsanded grouts above are made for joints up to 1/8 in; sanded grout covers wider joints, starting at 1/8 in for Keracolor S and Polyblend Plus Sanded or 1/16 in for LATICRETE 1500 Sanded. LATICRETE recommends unsanded grout for soft or polished marble, soft stone, some polished stone, and soft glazed tile at 1/8 in or less.

Is this the MAPEI grout calculator?

No, but its math uses MAPEI's published consumption formula, converted to inches and pounds. MAPEI's own charts differ by product, so if you buy a MAPEI grout, check the chart on its bag or data sheet.

How much grout do I need for a backsplash?

A 30 sq ft backsplash of 3 x 6 in subway tile, 1/4 in thick, with 1/8 in joints takes about 3.9 lb, or 4.3 lb with 10% extra: one 10 lb bag. MAPEI's Keracolor U chart lists 104 sq ft per 10 lb for that tile and joint, so it would need less.

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