How to Grout Tile: What to Buy and How Much You Need

Grout is the last step of a tile job and the first thing people notice when it's wrong. Too little grout and you're back at the store mid-project. Too much and you've got half a bucket drying in the garage. Here's how to buy the right type, calculate the right amount, and get a clean finish.

Sanded vs Unsanded Grout

Sanded grout contains fine silica sand. It's stronger, resists cracking, and works for grout lines 1/8 inch and wider. Use it on floors, shower walls with standard spacers, and any high-traffic area.

Unsanded grout is smooth (no sand). Use it for grout lines 1/8 inch or narrower — typically walls with 1/16-inch spacers, polished marble, or glass tile that scratches easily.

When in doubt on a floor, go sanded. On a shower wall with 1/8-inch lines, either works — sanded is more durable.

How Spacer Size Affects Quantity

Wider grout lines use more grout. The math depends on tile size, tile thickness, joint width, and total area. As a rough guide for a 100 sq ft floor with 12×12 tile:

For a 50 sq ft bathroom floor with 12×12 tile and 1/8-inch spacers, plan on 3 pounds of grout — which means buying one standard 5-lb container (you'll use most of it).

Larger format tile (24×24) uses less grout per square foot because there are fewer joints. Small mosaics on mesh backing use significantly more grout per square foot because of all the joints.

Grout Calculation Formula

The precise formula accounts for tile size, joint width, and joint depth:

Grout (lbs) = (A + B) × C × D × 1.58 ÷ (A × B) × sq ft

Where A = tile length (in), B = tile width (in), C = joint width (in), D = tile thickness (in).

For most DIYers, using a calculator is faster. The Tile & Grout Calculator handles this automatically — enter tile dimensions, spacer size, and room area.

How Much to Buy

Grout is sold in bags or tubs:

• 5 lb tub — small backsplash or powder room floor
• 10 lb bag — standard bathroom
• 25 lb bag — large floor or multiple rooms

Buy one size up from your calculation. Mixed grout doesn't store — you can't save leftovers for later. But running out mid-grout is worse, because matching the batch color later is unreliable.

Mixing Grout

1. Add powder to water, not water to powder — pour about 3/4 of the recommended water, add grout, mix, then add remaining water to reach peanut-butter consistency
2. Mix small batches — only as much as you can apply in 30 minutes
3. Let it slake — after mixing, wait 5–10 minutes, then remix without adding water. This allows chemicals to activate.
4. Don't over-water — runny grout is weak grout and causes efflorescence (white haze)

// TODO: affiliate link — margin trowel and a // TODO: affiliate link — rubber grout float (hard rubber for sanded, soft for unsanded) for application.

Application Tips for a Clean Finish

Work in sections. Apply grout diagonally across tiles at a 45-degree angle to the joints. Push firmly to pack joints completely — hollow joints crack and collect water.

Remove excess quickly. Wait 15–30 minutes (check grout label), then wipe diagonally with a damp sponge. Rinse the sponge frequently. Don't use a soaking wet sponge — it pulls pigment from the joints and weakens the grout.

Haze removal. A thin film appears after the grout cures. Buff it off with a dry microfiber cloth 2–4 hours later. For stubborn haze, use a grout haze remover after 24 hours.

Seal it. Cement-based grout needs sealer after curing (typically 48–72 hours). Epoxy grout doesn't. Sealer prevents staining — especially important on kitchen floors and shower floors.

Epoxy Grout: Worth It?

Epoxy grout costs 3–5× more than cement grout but is virtually stain-proof and waterproof. Consider it for:

• Shower floors (constant water exposure)
• Kitchen backsplashes behind stoves
• White or light-colored grout anywhere

It's harder to work with — it sets faster and is stickier. Budget extra time and have denatured alcohol ready for cleanup.

Common Grout Mistakes

1. Wrong type — unsanded on a 1/4-inch floor joint will crack
2. Under-packing joints — grout should be flush with the tile surface, fully packed
3. Walking on floor too soon — wait 24 hours before light foot traffic on floors
4. Grouting before thinset cures — wait 24 hours after setting tile
5. Skipping sealer — especially on light-colored grout in wet areas

Shopping List for a 50 sq ft Bathroom Floor

• 1 bag sanded grout (1/8" joints, color of choice) — 5–10 lbs
• Grout float
• Two buckets (mix + rinse water)
• Large sponges
• Grout sealer (after curing)
• Painter's tape for baseboards (optional but keeps edges clean)

Grout is cheap relative to tile — don't skimp. Calculate the amount, buy the right type for your spacer size, and use the Tile & Grout Calculator to get it right before you mix your first batch.