How this estimate works
Thinset coverage is a product and trowel input, not a fixed square foot allowance. A larger notch can use more mortar for the same tile area. Look for the coverage row for the exact trowel, bag size, substrate, and application. If your product gives a range, enter the lower coverage for a cautious bag count. The example value is arithmetic only; it does not describe every mortar bag.
Measure each rectangular tile section and add the sections. Subtract a truly open area such as a permanently untiled opening. Do not subtract small obstacles if tile cuts continue around them. The waste percentage applies to net area before dividing by per-bag coverage. The calculator rounds the final ratio upward because a supplier sells whole bags.
This number is an order estimate. It does not determine adhesive suitability, trowel selection, substrate preparation, or whether a mortar may be used in a particular location. Confirm those choices against your selected product instructions and installation plan. Keep a list of dimensions and the coverage line you used so you can update the estimate if the tile layout or trowel changes.
Keep a copy of your measurements and the product information used. Recheck both before ordering, especially after a layout or supplier change.
Read the full How to Measure Tile Area and Estimate Thinset Mortar Bags for measuring steps, worked examples, and common order mistakes.