Grout Calculator: How Much Grout Do I Need?
Grout is the material every tiler underestimates — and here is the trap: small tiles need far more grout than big ones, because what matters is total joint length, not floor area. This free grout calculator does the real math: enter your tiled area, tile size, joint width and depth, and it works out the grout weight you need, rounds it up to whole bags, and estimates the cost. Never mix a desperate second batch mid-job again.
Tile Grout Calculator
How to Use This Grout Calculator
Enter the total tiled area in square feet — for a floor, length × width; for shower walls, add up each wall. Then enter your tile size in inches. This matters more than anything else: a 12 × 12 tile has 24 inches of joint per square foot, while a 1 × 1 mosaic has 288.
Choose your grout joint width — 1/8 inch is the modern standard for rectified tile, 1/4 inch for rustic tile with irregular edges. Set the joint depth to your tile's thickness (about 1/4 inch for floor tile). Pick your bag size and a price for the cost estimate, then click Calculate.
The Grout Calculation Formula
The key insight: joint length per square foot = 144 × (1 ÷ tile width + 1 ÷ tile height) inches. The grout volume in cubic inches is then area × joint length × joint width × joint depth. Convert to pounds with the density of cement grout — about 0.084 lb per cubic inch (145 lb per cubic foot) — and add 10% waste: pounds = volume × 0.084 × 1.10. Finally, round up to whole bags.
Worked example: 100 square feet of 12 × 12 tile with 1/8-inch joints. Joint length: 144 × (1/12 + 1/12) = 24 inches per square foot. Volume: 100 × 24 × 0.125 × 0.25 = 75 cubic inches. Weight: 75 × 0.084 × 1.10 = 6.9 pounds — so one 25 lb bag covers the job with room to spare. The same floor in 4 × 4 tile would need about 21 pounds, still one bag; in 1 × 1 mosaic it would need over 80 pounds, or four bags.
Pro Tips for Grouting Like a Pro
Match the grout type to the joint: sanded grout for joints 1/8 inch and wider, unsanded for narrow joints and scratch-prone tiles like polished stone or glass. In showers and wet areas, spend the extra money on epoxy grout — it repels water, resists staining and never needs sealing.
Mix in small batches. Grout starts to set in 20 to 30 minutes, and you cannot revive a stiffening bucket by adding water — that weakens the cured grout. Work the float diagonally across the joints, wait until the grout hazes (about 15 to 30 minutes), then wipe with a damp sponge, rinsing it constantly. A too-wet sponge is the number one cause of washed-out, crumbly joints.
Frequently Asked Questions
How much grout do I need for 12x12 tile with 1/8-inch joints?
For every 100 square feet of 12x12 tile with 1/8-inch joints you need about 7 pounds of grout — one standard 25 lb bag covers roughly 350 square feet. Smaller tiles need much more grout because they have far more joint length.
What is the difference between sanded and unsanded grout?
Sanded grout contains fine sand for strength and goes in joints 1/8 inch and wider. Unsanded grout is smoother and is for narrow joints under 1/8 inch and soft tiles that would scratch. Epoxy grout is best for showers — it never needs sealing.
How much grout do I need per square foot?
It depends on tile size and joint width. Large 12x12 tiles with thin 1/8-inch joints need about 0.07 lb per sq ft, while 1x1 mosaic with the same joints needs roughly 0.85 lb per sq ft — twelve times as much.
How long does grout take to dry?
Light foot traffic after 24 hours, full cure after about 72 hours. Wait at least 7 days before sealing cement grout. Epoxy grout cures faster — usually ready for water in 24 hours.