Paint Coverage & Coat Planner

First, it assumes a baseline coverage of 350 sq ft per gallon, then adjusts for losses with an effective coverage value: effective_coverage = 350 × efficiency_index. Next, it recommends the number of paint coats based on surface type and sheen, and—if priming is selected or triggered by “Auto”—adds 1 primer coat and computes separate gallons for primer and topcoat.

This tool assumes uniform coverage across the stated area; if you have heavy patching, uneven texture, or unusually porous spots, real-world gallons may be higher. Sheen affects hiding difficulty in the model (e.g., semi-gloss/gloss tend to need more coats), and the efficiency index is your lever for real application conditions like cutting overhead, roller type, and waste.

If you select “Auto,” the calculator typically prompts for primer on unfinished wood, brick/CMU, and plaster/stucco, and it may still recommend primer when sheen increases hiding demand. If you override primer to “No primer needed” on a surface that usually requires it, the tool compensates by increasing coat counts—so you may end up buying more topcoat rather than primer.

Don’t rely on the paint’s label “coverage” for this tool—its built-in assumption is fixed at 350 sq ft per gallon and then adjusted by your efficiency index. Also, enter the actual surface area you plan to coat (sq ft); if you include unpainted sections or undercount patches/texture, the gallon estimate will be optimistic.