Grout Calculator
Estimate how many pounds of grout and how many bags to buy based on tile size, joint width, and joint depth.
Use unsanded grout for joints under 1/8 in, sanded for 1/8 in and wider. Joint depth is usually close to the tile thickness, roughly 1/4 in for thinner wall tile and 3/8 in for typical floor tile.
How it works
This uses the standard industry estimating formula for grout: (tile width plus tile height) times joint width times joint depth times 1.86, divided by the tile's area. That gives pounds of grout needed per square foot of tile, which the calculator then multiplies by your total area. Joint depth usually tracks the tile's thickness, so thinner wall tile and thicker floor tile call for different depth values even at the same joint width.
Worked example: 80 sq ft of 3x6 in subway tile with a 1/8 in joint at 1/4 in deep. The formula gives (3 + 6) × 0.125 × 0.25 × 1.86 ÷ (3 × 6), or about 0.029 lbs per sq ft. Multiply that by 80 sq ft and you get 2.3 lbs of grout, which rounds up to a single 10 lb bag with plenty to spare for touch-ups later. A bigger format like 12x12 in floor tile with a wider 1/4 in joint at 3/8 in deep needs a similar amount per square foot, since larger tiles have less joint length relative to their area even though the joint itself is wider.
FAQ
Should I buy sanded or unsanded grout?
Use unsanded grout for joints under 1/8 in, since the fine texture won't shrink or crack in a narrow gap. For joints of 1/8 in or wider, sanded grout holds up better and resists cracking as it cures.
Why does the calculator ask for joint depth separately from joint width?
Width and depth both add volume to the joint, so both affect how much grout you use. Depth is easy to overlook because it's set by the tile's thickness rather than a design choice, but skipping it in the math would badly undercount the total.
How much extra should I buy beyond the calculated amount?
The result already includes a reasonable buffer, but it's smart to round up to the next full bag anyway. Grout is cheap relative to the cost of a mid-project supply run, and leftover grout is worth keeping for repairs down the road.
Does grout color affect how much I need?
No, color doesn't change the formula. What matters is tile size and joint dimensions. Color is worth picking carefully for a different reason: it changes how forgiving the grout lines look over time as they pick up everyday grime.
For more on grout choices and upkeep, see how to choose grout color for bathroom tile, how to seal grout and why it matters, and how to regrout bathroom tile without replacing it.