Grout and Thinset Calculator
Enter your tile size, joint width and area to see how much grout and thinset to buy.
How the calculation works
Grout fills the joints between tiles. Every square foot of tile has a set length of joint, depending on tile size. That length times the joint width times the tile thickness is the volume of grout:
joint length per sq ft (in) = 144 × (tile length + tile width) ÷ (tile length × tile width)
grout (lb) = area × joint length × joint width × tile thickness × 0.069
The 0.069 is about how many pounds of mixed cement grout fill one cubic inch. The result includes 10% extra. Thinset uses typical coverage for a 50 lb bag at each trowel size, taken from common bag labels, plus 10% extra. Your bag's own coverage chart is the final word.
Worked example
100 sq ft of 12" × 12" tile, 3/8" thick, with 1/8" joints: there are 24 inches of joint per square foot, so the grout volume is 100 × 24 × 0.125 × 0.375 = 112.5 cubic inches. That's about 7.8 lb, or 8.5 lb with extra, so one 10 lb bag. With a 1/4" square-notch trowel, the thinset comes to 110 sq ft ÷ 95 sq ft per bag = 2 bags of 50 lb.
Tips
- Small tiles use far more grout. 2" mosaics need about six times the grout of 12" tiles for the same area.
- Sanded or unsanded: use unsanded grout for joints of 1/8" and narrower, and sanded grout for anything wider.
- Back-butter large tiles (15" and up) with a thin layer of thinset, so the bond covers the whole tile and there are no hollow spots.
Frequently asked questions
How much area does a 25 lb bag of grout cover?
It depends heavily on tile size and joint width. With 12" × 12" tile and 1/8" joints, a 25 lb bag covers roughly 300 square feet. With 4" × 4" tile and 1/4" joints, it covers only about 55 to 80 square feet, depending on tile thickness.
Which trowel size should I use?
As a rule, use a 3/16" V-notch for mosaics, a 1/4" × 1/4" square notch for tiles up to about 8", a 1/4" × 3/8" notch for tiles up to about 16", and 1/2" × 1/2" for larger tiles. Check the tile maker's instructions.