Frequently asked questions
The questions we get asked most about measuring, buying and installing tile.
How do I calculate how much tile I need?
Measure the area in square feet, divide by the square footage of one tile, then add 10–20% waste depending on the layout pattern. Buy in full boxes and keep one spare box.
How much extra tile should I order?
10% for straight layouts, 12% for offset, 15% for diagonal, and 20% for herringbone. Add 5% more if it is your first tile job.
How much grout will I need?
It depends on tile size, tile thickness and joint width. Small tile with wide joints can use five times the grout of large-format tile with tight joints — use the grout calculator for a real number.
How many bags of thinset per 100 sq ft?
Two 50 lb bags with a 1/4 x 3/8 in notched trowel. Three bags if you are using a 1/2 in notch for large-format tile, plus more if you back-butter.
Can I tile over existing tile?
Sometimes. The existing tile must be solidly bonded, flat and clean, and you must accept the added height at doorways and transitions. Use an appropriate bonding mortar, and never tile over cracked or hollow-sounding tile.
Do I need backer board under tile?
In wet areas, yes — cement backer board plus a waterproofing membrane. On floors, backer board or an uncoupling membrane over plywood; never tile directly onto a single layer of subfloor.
How long before I can walk on new tile?
Wait 24 hours before light foot traffic and 24–72 hours before grouting, following your mortar's label. Wait 7 days before heavy use or filling a shower with water.
What tile is safest for a wet floor?
Look for a DCOF (slip resistance) rating of 0.42 or higher, and use smaller tiles on a shower pan so the sheet can follow the slope.
Are these calculators free?
Yes, completely free with no sign-up. They run in your browser and we do not store your measurements.
How accurate are the results?
The math is exact, but real jobs vary. Treat results as a solid planning estimate and confirm quantities with your tile supplier before a large order.
· Reviewed by the Smart Tile Calculator editorial team