Coating coverage and paint estimating
Every coverage estimate starts from the same identity: one US gallon of solid material covers 1604 square feet at 1 mil dry. Everything after that is volume solids, target thickness, and honesty about losses.
Theoretical coverage = 1604 x volume solids fraction / DFT in mils, in square feet per gallon. A 70 percent solids product at 5 mils dry covers about 225 sq ft per gallon - before a single percent of loss. Verify volume solids on the current product data sheet; the project specification governs the target DFT.
From theoretical to practical
Real jobs lose paint to overspray, surface roughness and profile, dead volume left in pumps and lines, container residue, and irregular geometry that forces overlap. Divide theoretical coverage by (1 - loss fraction) or equivalently multiply the estimated gallons up.
Loss factors are job knowledge, not physics: airless spray on flat plate might lose 15 to 20 percent, conventional spray on lattice steel 40 percent or more, brush and roller relatively little. Your own past jobs are the best calibration; when in doubt, estimate ranges rather than a single number.
Estimating a work area
Take the coated area, divide by practical coverage, and round up to purchasable units per batch and per coat. Remember that each coat is its own calculation when thicknesses or products differ, and stripe coats consume material the area arithmetic does not show.
CoatSpec's product planner runs this arithmetic per work area from the coat system's solids, target DFT, area, and your loss allowance, and shows the WFT target alongside so application control and purchasing agree.
Frequently asked questions
How many square feet does a gallon of paint cover?
Theoretically, 1604 x volume solids fraction / DFT in mils. A 100 percent solids coating at 1 mil covers 1604 sq ft; a 60 percent solids coating at 4 mils covers about 241 sq ft. Practical coverage is always lower - divide by one minus your loss fraction.
What loss factor should an estimate use?
Typical territory runs 15 to 40 percent depending on application method, geometry, wind, and crew practice. Use records from similar past jobs where you have them, and state the assumed loss in the estimate so it can be challenged.
Do stripe coats change the estimate?
Yes. Stripe coating edges, welds, and bolts consumes material that plain area arithmetic does not capture. Estimators commonly add an allowance based on the length of edges and welds rather than trying to fold it into the area loss factor.