Module
One tile owns a rectangle of (tile + joint) by (tile + joint). Divide the floor by that rectangle. Round up. A 10 by 10 foot room is 100 square feet. Twelve-inch tile at 1/8 inch joint is a bit over 1 square foot each, so you need fewer than 100 tiles before waste, and more than 100 after a 10% cut allowance. Run the sheet. Do not do it in your head at the store.
Room area can start on the square foot calculator. Wood or laminate planks, with no grout joint, are the flooring calculator.
FAQ
Does the joint change the count?
Yes. A 12 inch tile with a 1/8 inch joint takes more than 1 square foot of floor. The module is 12.125 by 12.125 inches. Ignoring the joint over-orders by a little on large tile and by a lot on mosaic.
Where is the grout calculator?
On this page as a reminder, not a fake weight. Joint volume depends on depth and the sand in the grout. Read pounds per square foot off the grout bag for your joint width. Thinset is the same: the bag lists square feet per notch size.
Sources
- NIST Handbook 44: The inch and the square foot used to turn the tile module into area.