Paint Cost Calculator

Frequently Asked Questions

How much wall area does a gallon of paint cover?

About 350-400 square feet per gallon for one coat on smooth walls. Textured surfaces, primer, and dark-to-light changes can reduce coverage significantly.

How many coats of paint do I need?

Two coats is standard for even color and durability. One coat may suffice for touch-ups or premium paint over similar colors. Three may be needed over stark color changes.

Should I subtract doors and windows?

Yes, for accuracy on small rooms. A standard door is about 20 sq ft, a window about 15 sq ft. For large rooms, the rounding error is negligible.

How much extra paint should I buy?

Add 10-15% for waste, touch-ups, and future repairs. Save the leftover with the color code label so you can match later.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Buying paint is a balancing act: too little means a second trip to the store mid-project, too much wastes money on cans you will never open. This calculator turns your room dimensions into a confident gallon count. You enter the room's length, width, and ceiling height, the number of doors and windows to subtract, how many coats you plan to apply, the coverage rate printed on your paint can, and optionally a price per gallon. The tool computes the net paintable wall area, multiplies it by the number of coats, divides by coverage, and rounds up to whole gallons - then estimates your cost if you supplied a price.

Formula

Wall area = 2 × (length + width) × height. Net paintable area = wall area − (doors × 20 sq ft) − (windows × 15 sq ft), floored at zero. Total area to cover = net area × number of coats. Gallons needed = total area ÷ coverage rate, then rounded up with the ceiling function because paint is sold in whole cans. Estimated cost = gallons rounded × price per gallon.

Worked Example

A 14 ft × 12 ft room with 8 ft ceilings, 1 door, 2 windows, 2 coats, and 350 sq ft/gal coverage. Wall area = 2 × (14 + 12) × 8 = 416 sq ft. Subtract 1×20 + 2×15 = 50 sq ft, leaving 366 sq ft net. Two coats need 366 × 2 = 732 sq ft of coverage. Gallons = 732 ÷ 350 ≈ 2.09, rounded up to 3 gallons. At $35/gal that is about $105 of paint - buy an extra quart for touch-ups.

Common Mistakes

Using the smooth-surface coverage rate on textured or bare drywall - porous surfaces drop to 250-300 sq ft/gal, so lower the coverage input.

Forgetting that primer is effectively another coat - add it to the coat count or calculate it separately.

Skimping on coats for dark-to-light color changes - those almost always need two coats for even color.

Counting the ceiling - this tool computes walls only; figure ceiling area (length × width) on its own.

Rounding gallons down - running out mid-wall leaves lap marks; the tool always rounds up for this reason.

Tips & FAQ

What coverage should I enter? Most interior latex covers 350-400 sq ft/gal on smooth primed walls; check your can's label and reduce it for rough surfaces. One coat or two? One works when repainting a similar color; choose two for color changes, new drywall, or paints without built-in primer. What about trim and ceilings? Trim adds roughly 10-15% more paint and is usually a separate semi-gloss; ceilings need their own flat-white calculation. Which finish? Flat hides flaws on ceilings, eggshell or satin suits living areas, and semi-gloss resists moisture on kitchens, baths, and trim. Always buy one extra quart for touch-ups since coverage varies by brand and surface.

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