Coverage is for one coat
A label that says 350 square feet per gallon describes one coat under specified conditions. Two coats over 350 square feet require two gallons before adding an allowance. Do not confuse a room’s floor area with its wall area: a 10 × 12-foot room has a 120-square-foot floor, but its four 8-foot-high walls total 352 square feet.
Use the label, not a universal number
The same brand may sell products with different coverage rates. BEHR lists 250–400 square feet per gallon for certain interior products. Check the exact product’s documentation and choose a conservative value when the surface is porous or textured.
Read BEHR’s coverage guidance.
Keep different products separate
Walls, ceilings, trim and primer may require different products and application rates. Prepare an estimate for each. If multiple rooms share one color and product, total their unrounded requirements before rounding up to your available container sizes.
Make a shopping note
Record the color code, sheen, product name, coat count and estimated gallons. Keep your measurements with that note so you can revise the order if the chosen product has a different coverage rate.