Grout Calculator
Enter your tile dimensions, grout joint size, and total area to calculate how many bags of grout your project requires. Uses industry-standard coverage rates for 25 lb bags.
Estimate only — not professional advice. Always verify results independently before purchasing materials or beginning work. Terms of Use
What is Grout?
A grout calculator estimates the number of bags of grout needed to fill the joints between tiles in a floor, wall, or countertop installation. Grout fills the gaps between tiles, providing structural support, preventing moisture intrusion, and creating a finished appearance. Accurately estimating grout quantity prevents mid-project shortages (which can cause color variation between batches) and minimizes waste from over-purchasing. The amount of grout required depends on four variables: the total tiled area, tile size, joint width, and joint depth. Smaller tiles require dramatically more grout per square foot because they have more joint length per area. A floor of 2-inch mosaic tiles with 1/8-inch joints uses roughly 36 times more grout per square foot than the same floor with 24-inch tiles at the same joint width. The industry baseline for coverage is that one 25 lb bag of grout covers approximately 100 square feet of 12 x 12 inch tile with 1/8-inch wide by 1/4-inch deep joints. This baseline scales proportionally with tile size and joint dimensions. Smaller tiles, wider joints, or deeper joints all reduce coverage per bag. Larger tiles, narrower joints, or shallower joints increase coverage. There are two main types of grout: unsanded (non-sanded) and sanded. Unsanded grout is used for joints 1/8 inch or narrower, typically in wall tile and polished stone installations. Sanded grout is used for joints wider than 1/8 inch, most commonly in floor tile work. Epoxy grout is a third option that offers superior stain and water resistance but costs three to four times more and is harder to work with. Coverage rates are similar for sanded and unsanded at the same joint dimensions. Joint depth is determined by tile thickness — grout should fill the joint to within about 1/16 inch of the tile surface. Standard wall tiles are 1/4 inch thick, floor tiles are 3/8 to 1/2 inch thick, and natural stone can be 3/8 to 3/4 inch thick. The joint depth in this calculator represents the actual grout depth in the joint. Always buy 10-15% more grout than the calculated amount to account for waste during mixing, application, and cleanup. Grout has a long shelf life when stored dry, so leftover bags are useful for future repairs and re-grouting.
How to Calculate
- Measure the total area to be grouted in square feet
- Note the tile width and length in inches (as printed on the tile box)
- Determine the grout joint width — 1/8 inch is standard for most floor tile
- Determine the joint depth based on tile thickness (typically 1/4 inch for wall tile, 3/8 inch for floor tile)
- The calculator shows coverage per bag and total bags needed
- Add 10-15% extra for waste and future repairs
Formula
Coverage per 25 lb bag = 100 x (Tile Width / 12) x (Tile Length / 12) / (Joint Width / 0.125) / (Joint Depth / 0.25) Bags Needed = ceiling(Area / Coverage per Bag) The baseline of 100 sq ft per 25 lb bag applies to 12 x 12 inch tiles with 1/8 inch wide by 1/4 inch deep joints. The formula scales proportionally: doubling tile size doubles coverage, doubling joint width halves coverage, and doubling joint depth halves coverage.
Example Calculation
100 sq ft of 12 x 12 inch tile with 1/8 inch (0.125 in) wide by 1/4 inch (0.25 in) deep joints: Coverage = 100 x (12 / 12) x (12 / 12) / (0.125 / 0.125) / (0.25 / 0.25) Coverage = 100 x 1 x 1 / 1 / 1 = 100 sq ft per bag Bags = ceil(100 / 100) = 1 bag For the same area with 6 x 6 inch tiles and 1/4 inch joints: Coverage = 100 x (6 / 12) x (6 / 12) / (0.25 / 0.125) / (0.25 / 0.25) = 100 x 0.5 x 0.5 / 2 / 1 = 12.5 sq ft per bag Bags = ceil(100 / 12.5) = 8 bags
Frequently Asked Questions
What is the standard grout joint width for floor tile?
The standard grout joint width for floor tile is 1/8 inch (3 mm) for rectified (precision-cut) tiles and 3/16 inch for non-rectified tiles. Wider 1/4-inch joints are common with handmade tiles, natural stone, and rustic installations. Mosaic sheets typically have 1/16 to 1/8 inch joints. Never use joints narrower than 1/16 inch — the grout needs minimum width to bond properly.
When should I use sanded vs. unsanded grout?
Use unsanded grout for joints 1/8 inch or narrower — the sand particles in sanded grout are too large to fit into narrow joints and can scratch polished stone. Use sanded grout for joints wider than 1/8 inch — the sand provides structural strength that prevents cracking in wider joints. For joints exactly 1/8 inch, either type works, but sanded is the safer choice for floors.
How long does grout take to dry?
Grout should be left undisturbed for 24 hours after application. It reaches initial hardness in 24-48 hours, at which point you can walk on the floor with care. Full cure takes 28 days, during which the grout should be kept dry. Do not seal grout until it has cured for at least 72 hours, and ideally 7-14 days. Sealing too early traps moisture and prevents proper curing.
Should I seal my grout?
Yes, cement-based grout (both sanded and unsanded) should be sealed after curing to prevent staining and moisture absorption. Apply a penetrating grout sealer 7-14 days after grouting, and re-seal annually for floors and every 2-3 years for walls. Epoxy grout does not require sealing — it is naturally non-porous and stain-resistant.
How do I calculate grout for a shower?
Calculate each surface separately — floor, walls, ceiling (if tiled), and niche shelves. Add the areas together for the total. Shower walls typically use 1/16 to 1/8 inch joints with unsanded grout. Shower floors (especially mosaic) may use wider 1/8 inch joints with sanded grout. Use the appropriate joint width for each surface in your calculation.
Why does my grout crack after drying?
The most common causes of grout cracking are: joints too wide for unsanded grout (use sanded for joints over 1/8 inch), too much water in the mix (grout should be the consistency of peanut butter), tile movement from an insufficiently rigid substrate, and rapid drying from heat or air circulation. Hairline cracks in the first 48 hours can sometimes be repaired by dampening the surface and working additional grout into the joints.