TileQuantCoverage math for tile, thinset and grout — before you buy.

Grout for 30 ft² of 12×12″ tile with 3/8″ joints

Grout needed
6.4lb
1 × 25 lb bags for 30 ft² of 12″ × 12″ with 0.375″ joints
25 lb bags1bags
10 lb bags1bags
Dry grout weightincludes 10% waste6.4lb
Grout volume0.06ft³
Joint lengththis, not the floor area, is what drives the quantity60linear ft
Joint depththe tile thickness for 12″ × 12″0.375in
Grout type0.375″ is ⅛″ or widerSanded
Area
30 ft²
Tile size
12×12″
Joint width
3/8 in

Grout follows joint length, not floor area

This is the calculation people get wrong, and they get it wrong in a predictable direction. Grout fills the space between tiles, so what matters is the total length of joint — and that goes up as the tile gets smaller.

30 ft² of 12×12″ tile has 60 linear ft of joint. At 3/8″ wide and 0.375″ deep that is 6.4 lb of dry grout, or 1 × 25 lb bags.

Any estimate quoted as "pounds per square foot" without asking the tile size is a guess. The same floor in 2″ mosaic eats several times this.

sanded grout, and it is not a preference

At 3/8″ the answer is sanded. Joints ⅛″ and wider take sanded grout — the sand is structural and stops the grout shrinking and cracking as it cures. Narrower than that, sand physically cannot pack in, and forcing sanded grout into a tight joint leaves voids behind a surface that looks fine.

Unsanded also goes on polished stone and glass regardless of joint width, because sand scratches the face.

Buy one bag more than this

Running out mid-floor is worse than it sounds. The second batch cures at a different rate and often dries a visibly different shade — colour lots vary between bags, and so does how long the mix sat before it went down.

Notes

  • Grout follows joint length, not floor area. 30 ft² of 12″ × 12″ has 60 linear ft of joint; the same floor in 2″ mosaic would have roughly 360 ft and eat several times the grout. Any estimate given as "pounds per square foot" without asking the tile size is guessing.
  • Sanded grout at 0.375″. The sand is structural — it stops the grout shrinking and cracking as it cures across a wide joint.
  • Buy one more bag than the number here. Running out mid-floor means the second batch cures at a different rate and often dries a visibly different shade — colour lots vary, and so does how long the mix sat.
  • Joint depth is assumed equal to the tile thickness (0.375″). If the thinset squeezed up into the joints, the real depth is less and you will use less grout than this — clean the joints out before the thinset sets rather than grouting over it.

Nearby sizes