How this calculator works
Grout fills the joints between tiles, so the amount depends on how much joint there is, not just on the area. Small tiles mean more joints per square foot; wider and deeper joints hold more grout. The calculator works out the joint volume, converts it to weight and rounds up to bags.
It uses the standard joint-volume formula and assumes about 112 lb per cubic foot of packed cement grout. Joints of ⅛″ (3 mm) and wider get sanded grout; narrower joints get unsanded.
joint volume per sq ft (in³) = 144 × (L + W) ÷ (L × W) × joint width × depth
grout lb = area × joint volume per sq ft × 0.065 lb/in³ × (1 + waste)
L and W are the tile length and width in inches; depth is the tile thicknessWorked example
A 10′ × 8′ bathroom floor is 80 sq ft. With 12″ × 12″ tile, ⅛″ joints and ⅜″ thick tile, each square foot has 144 × 24 ÷ 144 × 0.125 × 0.375 = 1.125 cubic inches of joint. 80 sq ft holds 90 cubic inches, about 5.9 lb of grout; with 10% waste that is 6.4 lb, so one 10 lb bag of sanded grout covers it.
Tips before you buy
- Mix only as much grout as you can spread and clean in about 20–30 minutes, and work in small sections.
- Buy all the grout for one job from the same color and batch; colors can vary slightly between batches.
- Let cement grout cure before sealing it; the bag states how long to wait.
- Rake out spacers and any thinset that squeezed into the joints before grouting, so the grout has full depth.
Questions
- Sanded or unsanded grout?
- Use sanded grout for joints ⅛″ (3 mm) and wider; the sand keeps wide joints from shrinking and cracking. Use unsanded grout for narrower joints, which are common on wall tile and polished stone that sand could scratch.
- How much area does a 25 lb bag of grout cover?
- It depends almost entirely on tile size and joint width. By the formula used here, with ⅛″ joints ⅜″ deep a 25 lb bag fills roughly 340 sq ft of 12″ tile but only about 55 sq ft of 2″ mosaics, before waste. Enter your own sizes to see the difference.
- Why does small tile need so much more grout?
- Every tile is surrounded by joint. Halving the tile size roughly doubles the length of joint per square foot, so mosaics and small hex tiles use several times as much grout as large-format tile.
- What about epoxy grout?
- Epoxy grout is sold in kits by volume and is denser than cement grout. Use the joint volume from this calculator as a guide, then check the coverage table on the kit you choose.