Tile Grout & Spacer Calculator: Grout Weight, Bags, Tiles and Spacers
Estimate the grout and tile spacers for a tiling job: grout weight and bags from tile size, joint width and depth with the manufacturers’ formula, grout per square foot, tiles with waste and boxes, spacer count by layout, and a grout table for common joint widths.
How it works
Grout volume = area × (L + W) ÷ (L × W) × joint width × joint depth · Grout weight = volume × grout factor (about 1.6 kg/L = 100 lb/cu ft for cement grout) · Bags = ⌈weight × (1 + waste) ÷ bag size⌉ · Tiles = area ÷ [(L + joint) × (W + joint)] · Spacers ≈ tiles × spacers per tile × 1.1
Grout fills the joints around each tile, so its volume is the joint length per unit of area times the joint width and depth. A tile of length L and width W has (L + W) of joint per L × W of surface, which gives the formula grout makers publish: volume per unit area = (L + W) ÷ (L × W) × joint width × depth. Multiply by the tiled area and by the grout factor on the bag (the dry powder needed per litre of joint, about 1.6 kg/L or 100 lb per cubic foot for cement grout) to get the weight to buy. The formula ignores the small squares where joints cross, which makes it a little generous, as an ordering figure should be. Tile size and joint width drive the result: halving the tile size doubles the grout, and doubling the joint doubles it too, which is why mosaics with wide joints use so much. Depth is normally the tile thickness. Tiles are counted with each tile’s share of the joint, and the waste allowance is added to both tiles and grout. Spacer counts depend on how you use them. Standing spacers upright in the joints, two along each edge, takes about four per tile; laying cross spacers flat at each corner takes about one per tile because four tiles share each corner. The count adds 10% for spacers that get lost or broken.
Worked example
With the defaults, 100 sq ft (14,400 sq in) of 12 × 12 in tile, 3/8 in thick, with a 1/8 in joint: (12 + 12) ÷ (12 × 12) × 0.125 × 0.375 = 0.0078125 cu in of grout per sq in, so 14,400 × 0.0078125 = 112.5 cu in = 1.844 L. At 1.6 kg/L that is 2.950 kg = 6.50 lb of grout, or 7.15 lb with 10% waste: one 25 lb bag. With the joint, each tile takes 12.125 × 12.125 = 147.0 sq in, so 14,400 ÷ 147.0 = 98 tiles (108 with 10% waste) and 97.9 × 4 × 1.1 = 431 spacers used upright.
Sources: Omni Calculator: Grout calculator (joint-area geometry, 1,600 kg/m³ average density) · Sika: SikaCeram tile grout data sheet (coverage formula, density about 1.6 kg/L) · Tilers Forums: How to calculate your grout requirements (300 × 300 mm, 4 mm joint, 10 mm deep = 0.426 kg/m²; product grout factors 1.4–1.75) · CalcForLife: Grout calculator UK (per-m² formula, density by grout type)
Frequently asked questions
How much grout do I need per square foot?
For 12 × 12 in tile, 3/8 in thick, with a 1/8 in joint, about 0.065 lb per sq ft, so a 25 lb bag covers roughly 350 sq ft. For 4 × 4 in wall tile with the same joint it is about three times as much, and 2 × 2 in mosaics take about six times as much.
What formula do grout manufacturers use?
Most publish kg/m² = (A + B) ÷ (A × B) × C × D × 1.6, where A and B are the tile length and width in mm, C the tile thickness in mm, D the joint width in mm and 1.6 the grout factor in kg/L. This calculator uses the same formula in any units.
How many spacers do I need?
About four per tile if you stand spacers upright in the joints (two along each edge), or about one per tile if you lay cross spacers flat in the corners, since four tiles share each corner. Add about 10%, and remember most can be pulled and reused as you work.
Sanded or unsanded grout?
Use unsanded grout for joints narrower than 1/8 in (3 mm) and for polished stone or glass that sand could scratch. Use sanded grout for joints of 1/8 in and wider; the sand stops the grout from shrinking and cracking.
What joint width should I use?
Rectified porcelain can go as narrow as 1/16 in, but 1/8 in is common for floors and 1/16 in for walls. Handmade or cushion-edged tile needs 3/16 to 1/4 in or more to absorb size variation. Check the tile maker’s minimum joint.
Should I buy extra tile too?
Yes: add 10% for straight layouts and 15–20% for diagonal or patterned layouts to cover cuts, breakage and future repairs. Keep a box from the same lot for repairs later.
Related calculators
Estimates only: add a margin for waste and follow the grout and tile manufacturers’ instructions.