Grout Calculator
Grout volume from tile size and joint width, with order quantity.
What it does
Grout quantity hides in the joints. A hundred square feet of 12 inch tile with quarter inch joints needs under a gallon, while the same area in 6 inch tile needs roughly double, because joint length per square foot doubles as tile shrinks. Guessing buys either a second store run or a wasted half bag.
The tool above runs both unit systems. Imperial mode takes square feet, tile inches, and joint decimals, and prints gallons and liters. Metric mode takes square meters, tile centimeters, and joint millimeters. Defaults mirror each other, and every run adds the 10 % waste order quantity beside the neat volume.
Trade rules set the mix choice. The Tile Council of North America states joints under 1/8 in take unsanded grout only, 1/8 in and up take sanded only, and joints past 3/8 in need heavily sanded or wide joint mixes. NIST volume definitions supply the 231 in3 gallon and 61.0237 in3 liter used for conversion.
Depth is the quiet input. Joints filled shallow crack and stain early, so depth usually equals tile thickness. Measure a set tile edge, enter that depth, and let the waste factor cover tooling and cleanup losses.
How to use
- Pick imperial (ft, in) or metric (m2, cm, mm).
- Enter the tiled area.
- Enter tile length and width.
- Enter joint width as a decimal: 1/4 in is 0.25.
- Enter joint depth, often the tile thickness.
- Read volume, then the +10 % order quantity. Pick sanded or unsanded by the width rule.
Formula
- area
- Tiled area: sq ft or m2.
- joint width
- Joint width: inches or mm. Under 1/8 in uses unsanded.
- depth
- Joint depth, often the tile thickness.
- tile L, W
- Tile length and width in matching units.
All inputs convert to meters inside; the 61.0237 in3 per liter and 231 in3 per gallon factors come from NIST definitions. Metric defaults mirror the imperial ones.
Worked example
Example: 100 sq ft of 12 in tile
Imperial defaults: 100 sq ft of 12 inch tile with 1/4 in joints 3/8 in deep.
- Inputs: 100 sq ft, 12 x 12 in tile, 1/4 in joints, 3/8 in deep.
- Area: 100 x 144 = 14,400 in2. Joint factor: 1/12 + 1/12 = 1/6.
- Volume: 14,400 x 0.25 x 0.375 / 6 = 225 in3.
- Convert: 225 / 231 = 0.97 gal; 225 / 61.0237 = 3.69 L.
- With 10 % waste: 1.07 gal. Tool shows 0.97 gal, 3.69 L, 1.07 gal +10%.
Reference table
| Joint width | Mix | Note |
|---|---|---|
| Under 1/8 in | Unsanded only | Tight joints, soft tile safe |
| 1/8 in and up | Sanded only | Standard floors and walls |
| Over 3/8 in | Heavily sanded / wide joint | Check maker amounts |
| Marble, polish prone | Unsanded at 1/16 in | Sanded can scratch |
Limits
- Fresh joints only. Repairs and regrouting vary with removal depth.
- Assumes even joints; lippage and wavy walls drink more.
- Maker coverage rates differ by mix; check the bag against this volume.
- Waste factor is a flat 10 %, not a job measured allowance.
Common mistakes
- Entering joint width as a fraction the tool cannot parse; use decimals.
- Using tile thickness wrong: shallow depth undercounts.
- Buying neat volume with no waste factor.
- Putting sanded grout in 1/16 in joints.
- Mixing sanded and unsanded on one floor and getting shade bands.
Try it yourself
Quick checks. Answers sit tucked under each question.
50 sq ft of 6 in tile, 3/16 in joints, 1/4 in deep?
Area 7,200 in2. 7,200 x 0.1875 x 0.25 / 3 = 112.5 in3 = 0.49 gal, 1.84 L.
10 m2 of 15 cm tile, 5 mm joints, 6 mm deep?
V = 10 x 0.005 x 0.006 x 13.333 = 0.004 m3 = 4 L, 1.06 gal. Order 4.4 L.
Questions
How is grout volume figured?
Tiled area times joint width times depth times the joint density (1/tile length + 1/tile width). Small tile with wide joints drinks grout fast.
Sanded or unsanded grout?
Under 1/8 in takes unsanded only; 1/8 in and up takes sanded only; past 3/8 in needs heavily sanded or wide joint mix, per TCNA.
How much waste should I add?
About 10 %. The tool prints the +10 % order quantity next to the neat volume.
Does small tile need more grout?
Yes, roughly double. Halving tile size doubles joint length per square foot at the same joint width.
What joint depth should I enter?
Often the tile thickness. When unsure, use full tile thickness as depth; shallow fills crack early.
Does tile type change the mix?
Yes. Marble and soft glaze scratch under sanded grout, so makers and TCNA steer them to tight joints with unsanded mix.
Sources
- Tile Council of North America: Grout FAQ
- NIST: SI Units, Volume
- NIST: Gallon definition (231 cubic inches)