Tile Grout Calculator
Grout for a whole tiling job: up to three areas (floor, walls, backsplash or mosaic) each with its own tile size, thickness and joint width, giving pounds or kilograms, bags, cost, joint length for sealing and a comparison of grout use across common tile sizes.
How it works
joint share = joint × (tile L + tile W) ÷ ((tile L + joint) × (tile W + joint)) · cu in per sq ft = 144 × joint share × joint depth · grout lb = cu in ÷ 1,728 × density × area, summed over each area · with waste = × (1 + waste%) · bags = ⌈grout ÷ bag size⌉ · joint length per sq ft = 12 × (L + W) ÷ ((L + joint)(W + joint))
Grout only fills the joints, so the amount depends on how much of each square foot is joint. That share rises as tiles get smaller and as joints get wider. Each tile with its joint takes up (L + joint) × (W + joint), and the joint strip along two of its edges is joint × (L + W). Their ratio is the joint share, the same method manufacturers use for their coverage charts. The share times the joint depth (the tile thickness) gives a volume per square foot, and the grout density turns that into weight. About 112 lb/ft³ (1.8 kg/L) for sanded grout reproduces the published bag coverages. Real jobs often mix tiles, for example a 12 × 12 floor, 3 × 6 subway walls and a mosaic niche. Each area is worked out separately with its own tile and joint and then added up, and the mixed-joint warning tells you when you need two kinds of grout. A waste allowance covers what stays in the bucket and on the sponge. Bags are rounded up to whole units.
Worked example
100 sq ft of 12 × 12 in tile, 3/8 in thick, with a 1/8 in joint: joint share = 0.125 × 24 ÷ (12.125 × 12.125) = 2.04%. That is 144 × 0.0204 × 0.375 = 1.10 cu in of joint per sq ft, or 110 cu in in all. At 112 lb/ft³ that is 110.2 ÷ 1,728 × 112 = 7.1 lb, and 7.9 lb with 10% waste, which is one 25 lb bag. A bag covers about 318 sq ft once waste is allowed for (350 sq ft without). Add 60 sq ft of 3 × 6 in subway on the walls, 5/16 in thick with a 1/16 in joint, and the walls need about 5.3 lb more before waste. Their narrow joints take unsanded grout.
Sources: Custom Building Products — Polyblend sanded grout coverage chart (TDS-129) · Omni Calculator — grout volume from tile and gap size · MAPEI — grout quantity calculator (tile size, thickness, joint)
Frequently asked questions
Do smaller tiles use more grout?
Yes, much more. A 2 × 2 in mosaic has about six times the joint per square foot of a 12 × 12 in tile at the same joint width. The comparison table under the results shows the difference for your joint and thickness.
What joint width should I use?
It depends on the tile and the look you want. Use 1/16–1/8 in for rectified and wall tile, 1/8–3/16 in for most floor tile, and 1/4–3/8 in for rustic or handmade tile that varies in size. Wider joints need more grout, and joints of 1/8 in and over usually take sanded grout.
Can I grout the floor and the walls from the same bags?
Only if the joints suit the same grout. Floors with 1/8 in or wider joints take sanded grout, while 1/16 in wall joints need unsanded. The calculator flags mixed joints. An epoxy or urethane grout rated for both widths lets you use one product.
Should I round up when buying grout?
Always. Add about 10% for waste, then round up to whole bags. Mixing a second small batch partway through the job can leave a visible color difference, so buy from one batch.
How is this different from the grout calculator?
This page plans a whole job with up to three areas, each with its own tile and joint, and compares grout use across tile sizes. The grout calculator covers a single area in more depth, with grout types and coverage by joint width.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.