Grouting Plan

The job

Date

Room

Area

Tile L

Tile W

Tile thickness

Joint width

Sanded or unsanded

LB NEEDED

Bag size

BAGS

Colour

Batch/lot no.

Figures and rules

Sanded grout density

104 lb per cu ft

Formula (inches)

(L+W) x joint x thickness / (L x W) / 12 x 104

Why (L+W)

each tile owns HALF of each of 4 edges

12x12, 1/4 thick, 1/8 joint

4.5 lb per 100 sq ft

12x12, 1/4 thick, 3/8 joint

about 13 lb per 100 sq ft

3x6 subway, 1/16 joint

about 7 lb per 100 sq ft

⚠ Halve the tile size

roughly DOUBLES the grout

⚠ Double the joint width

exactly doubles the grout

Unsanded grout

joints UNDER 1/8 in

Sanded grout

1/8 in and WIDER

1/16 in

0.0625

1/8 in

0.125

3/16 in

0.1875

1/4 in

0.25

⚠ Colour

depends on water and cure — buy ONE batch

Grouting day

• Thinset fully cured — check the bag, usually 24 hours
• Spacers removed, every one of them
• Joints raked out clean and free of thinset
• Tile edges wiped — dust ruins adhesion and colour
• Correct grout for the joint width (sanded vs unsanded)
• ALL bags from the same batch number
• Water measured, not eyeballed — it sets the colour
• Mixed, slaked for the stated time, remixed
• Worked diagonally across the joints with the float
• Excess struck off before it sets
• Haze removed at the right moment, not the next day
• Sealed if the grout is cementitious and the area gets wet

Tile size drives this, not room size

Grout fills joints. Halving the tile size roughly doubles the grout, because the term is (L+W)/(LxW). A mosaic floor and a large-format floor of identical area are completely different grout jobs.

Measure the tile's thickness

That is the joint DEPTH, and it is the input most often guessed. Wall tile at 1/4 in and porcelain floor at 3/8 in differ by 50% in grout with everything else the same.

Buy one batch, and one bag spare

Grout colour depends on the water in the mix and how it cured, so a second batch mixed later can be visibly different. A mismatched patch is permanent without regrouting. Spare bags are cheap.