How Much Grout Do I Need? Complete Guide

Grout quantity depends on four variables: tile size, joint width, tile thickness, and grout type. Get any of them wrong and you'll either run short mid-project (a problem when dye lots change between batches) or waste money on bags you don't need. Here's exactly how to calculate it.

The Grout Formula

The industry-standard calculation from the TCNA Handbook works like this:

Grout weight (lbs) = [(Tile Length + Tile Width) / (Tile Length × Tile Width)] × Joint Width × Tile Thickness × 144 × Area (sq ft) × Grout Density

That's the precise formula. In practice: use the Grout Calculator and enter your tile dimensions, joint width, and total area — it handles the math and converts to bag count automatically.

The most important insight: joint width has far more impact than tile size. A 1/4-inch joint on 12x12 tile uses roughly twice as much grout as a 1/8-inch joint on the same tile. Choose your joint width intentionally, not by default.

Grout Needed by Tile Size — Quick Reference

Tile Size	Joint Width	Lbs per 100 sq ft	10 lb bags needed	25 lb bags needed
2x2" mosaic	1/8"	~35 lbs	4 bags	2 bags
4x4"	1/8"	~18 lbs	2 bags	1 bag
6x6"	3/16"	~14 lbs	2 bags	1 bag
12x12"	1/8"	~8 lbs	1 bag	1 bag
12x12"	1/4"	~11 lbs	2 bags	1 bag
12x24"	1/8"	~6 lbs	1 bag	1 bag
12x24"	1/4"	~9 lbs	1 bag	1 bag
18x18"	3/16"	~7 lbs	1 bag	1 bag
24x24"	1/4"	~7 lbs	1 bag	1 bag

All figures per 100 sq ft, including 10% waste. Actual usage varies by tile porosity, application technique, and grout consistency.

Sanded vs. Unsanded vs. Epoxy Grout

Choosing the wrong grout type is one of the most expensive tiling mistakes — sanded grout on polished marble permanently scratches the surface.

Type	Joint Width	Best For	Sealing	Cost (10 lb bag)
Sanded cement	1/8" and wider	Floors, natural stone, most tile	Required annually	$10–$18
Unsanded cement	Under 1/8"	Wall tile, glass, polished stone	Required annually	$12–$20
Epoxy (2-part)	Any width	Showers, pools, kitchens, commercial	Never — stain-proof	$30–$50

The rule is simple: if the joint is 1/8 inch or wider, use sanded. If it's narrower, or if the tile surface is polished stone or glass, use unsanded. If you want a maintenance-free grout that never needs sealing, use epoxy.

How Much Grout for Common Projects

Project	Typical Area	Tile Size	Bags Needed
Kitchen backsplash	20–40 sq ft	3x6" subway	1–2 × 10 lb bags
Small bathroom floor	35–50 sq ft	12x12"	1 × 10 lb bag
Standard bathroom floor	50–80 sq ft	12x12"	1 × 25 lb bag
Shower walls + floor	80–120 sq ft	4x4" or 12x12"	2–3 × 10 lb bags
Kitchen floor	100–200 sq ft	12x24"	1–2 × 25 lb bags
Large living area	300–500 sq ft	24x24"	2–4 × 25 lb bags

Tips to Get the Right Amount

Always buy at least 10% more than calculated. Grout is produced in batches and the color can vary between production runs — running short and buying another bag from a different batch can result in a visible color mismatch in the finished tile work.

For epoxy grout, buy exactly what you need or slightly under — mixed epoxy cannot be saved and unused portions are wasted. Work in small sections (about 10 sq ft at a time) because epoxy sets faster than cement grout.

Large-format tile (18 inches or larger) uses surprisingly little grout because the joint-to-tile ratio is so low. Don't overbuy based on area alone — check the table above first.

Frequently Asked Questions

How much grout do I need for a 100 square foot floor with 12x12 tile? With 1/4-inch joints, you need about 11 lbs of grout. One 10 lb bag plus a buffer — buy two 10 lb bags or one 25 lb bag.

How many bags of grout for a shower? A typical shower with 4x4-inch tile on walls and floor (80–120 sq ft total) needs 2–3 bags of 10 lb unsanded grout. Use the Grout Calculator for your exact dimensions.

Can I use the same grout for floors and walls? Yes, if the joint width and tile type allow it. Use sanded grout for floor joints 1/8 inch and wider. Use unsanded grout for wall tile with narrow joints (under 1/8 inch) to avoid scratching the tile surface.

How long does a bag of grout cover? A 10 lb bag of sanded grout covers approximately 90–100 sq ft at 1/8-inch joints with 12x12 tile. Coverage drops significantly with smaller tiles, wider joints, or more porous grout types.