How to Use This Grout Calculator
Enter the floor or wall area you are tiling, pick a common tile size (or type your own length and width), then add your grout joint width and tile thickness. Choose the grout type, set a waste allowance with the slider, and enter the size of the bag you plan to buy. Press Calculate to see total grout in pounds and kilograms, bags to buy, leftover, coverage per bag, and a table comparing different joint widths for the same tile.
Why This Matters
Grout is one of those materials you only think about at the very end of a tile job, which is exactly when running short hurts. Grout colors can vary slightly between production lots, so a second bag from a different batch may not match the first, and you cannot easily stop mid-floor while the mix sets. Over-buying has a cost too: epoxy grout kits often cost several times as much as cement grout, and a few unneeded kits add up fast.
Tile size drives the answer more than most people expect. A 100 sq ft bathroom floor in 12×12 tile with 1/8 in joints needs only about 7 lb of grout. The same room in 2×2 mosaic needs roughly 43 lb, more than six times as much, because there are far more joint lines per square foot. Joint width and tile thickness scale the quantity in a straight line: double either one and you double the grout.
Tilers use this kind of estimate when quoting jobs, homeowners use it to buy the right number of bags in one trip, and renovators use it to compare joint widths before choosing a tile layout. Pairing it with a sensible waste factor keeps you covered for spillage, sponge loss and the extra grout that sinks into porous or uneven tile edges.
How It's Calculated
The calculator uses the standard volumetric estimating formula found in many grout manufacturers' guides. All dimensions are converted to inches internally:
Weight (lb) = Volume (in³) ÷ 1,728 × density (lb/ft³)
Total (lb) = Weight × (1 + waste %)
Bags = Total ÷ bag size, rounded up
L and W are the tile length and width, J is the joint width and T is the tile thickness, which sets the grout depth. The fraction (L + W) ÷ (L × W) is the length of joint per unit of tile area. Multiply it by the area and you get total joint length; multiply by J and T and you get the volume of the joint channel.
Density is the planning figure for dry grout per cubic foot of finished joint: about 100 lb/ft³ for sanded cement grout, 95 for unsanded, and 105 for epoxy. Real products differ, so treat these as typical values. Metric inputs use 1 in = 25.4 mm, 1 m² = 1,550 in² and 1 lb = 0.4536 kg.
The formula ignores the tiny corner term J², so it slightly over-estimates, which is the safe direction. Bag counts are always rounded up, never down. Remember this is a materials estimate, not a specification: installation methods are covered by standards such as ANSI A108/A118 and the TCNA Handbook, and manufacturer coverage charts and local requirements vary. Check the label on the product you buy.
Worked Example
Suppose you are tiling 100 sq ft with 12×12 in sanded-grout tile, a 1/8 in (0.125 in) joint, 3/8 in (0.375 in) tile thickness, 10% waste and 10 lb bags.
- Area in square inches: 100 × 144 = 14,400 in².
- Joint length per unit area: (12 + 12) ÷ (12 × 12) = 0.1667.
- Volume: 14,400 × 0.1667 × 0.125 × 0.375 = 112.5 in³ (0.0651 ft³).
- Weight at 100 lb/ft³: 0.0651 × 100 = 6.51 lb.
- Add 10% waste: 6.51 × 1.10 = 7.16 lb (3.25 kg).
- Bags: 7.16 ÷ 10 = 0.72, rounded up to 1 bag with about 2.84 lb left over.
Switch the tile to a 2×2 in mosaic with the same joint and thickness and the volume jumps to 675 in³, or about 43 lb with waste, which means 5 bags of 10 lb.
Tips & Common Mistakes
- Measure the tiled area, not the room. Subtract tubs, islands and cabinets, but keep waste at 10% or more for cut-heavy layouts.
- Use the real tile thickness. Thick porcelain pavers and stone (1/2 in or more) need much more grout than 1/4 in wall tile. Measure one tile edge with a ruler.
- Match grout to joint width. Sanded grout is generally used for joints wider than 1/8 in, and unsanded for 1/8 in or narrower and for easily scratched surfaces. Follow the manufacturer's range.
- Buy everything from one lot. Check the lot number on every bag so the color stays consistent across the room.
- Protect yourself. Sanded and cement grouts contain silica and are alkaline, so wear a dust mask, gloves and eye protection when mixing. Ventilate well when working with epoxy.
- Add extra for rough or tumbled tiles. Uneven edges, wide lippage and porous surfaces absorb more grout than the formula assumes.
Frequently Asked Questions
How much grout do I need per square foot?
It depends on tile size, joint width and thickness. For 12×12 tile with 1/8 in joints and 3/8 in thickness it is about 0.065 lb per sq ft before waste. For 2×2 mosaic with the same joint and thickness it is roughly 0.39 lb per sq ft.
How many square feet does a 10 lb bag of grout cover?
Using the examples above with 10% waste, a 10 lb bag covers about 140 sq ft of 12×12 tile but only about 23 sq ft of 2×2 mosaic. The calculator shows the coverage per bag for your exact inputs. Bag labels often quote a single best-case figure.
Do I need sanded or unsanded grout?
As a general rule, sanded grout is used for joints wider than 1/8 in because the sand resists shrinking and cracking. Unsanded grout suits narrow joints and delicate surfaces such as polished marble or glass. Always confirm with the grout manufacturer's instructions.
How much extra grout should I add for waste?
The default is 10%, which suits most standard jobs. Use 15–20% for natural stone, hand-made or irregular tiles, and for complicated layouts. Precisely made rectified tile with narrow joints can get by with around 5%.
Does tile thickness really matter?
Yes. Grout fills the joint to the full depth of the tile, so the volume is directly proportional to thickness. A 3/4 in thick paver needs twice the grout of a 3/8 in tile with the same size and joint width.
Can I use this grout calculator for epoxy grout?
Yes, select epoxy to apply a typical density of 105 lb/ft³. Epoxy is usually sold in fixed-size kits, so enter the kit weight as the bag size and compare the result with the yield printed on the kit.