How much paint do I really need?

We multiply your wall perimeter by ceiling height to get wall area, subtract 21 sq ft per door and 15 sq ft per window, then divide by the industry-standard 400 sq ft per gallon coverage. Ceilings use floor area. Trim uses baseboard length + door/window casing measurements. We multiply by the number of coats you picked, then add your waste buffer (default 10%), and round up to whole gallons.

A rough surface has more area than a flat one, with tiny peaks and valleys the paint has to cover. Light orange-peel texture reduces coverage by about 15%. Heavy knockdown or popcorn can reduce it 30% or more. We apply these reductions automatically when you pick a texture. The same texture is applied to walls and ceiling (most homes share a finish across both); if yours differ, pick whichever is rougher.

Three situations: (1) new or patched drywall is porous and will drink paint without primer; (2) dramatic color changes like white over dark red need primer to prevent bleed-through and save a coat; (3) water stains, nicotine residue, or glossy/oil-based surfaces need a stain-blocking or bonding primer so the paint sticks and the stain doesn't ghost through. If none of those apply, a modern paint-and-primer-in-one is usually fine.

Often yes. A gallon of premium paint like Behr Marquee or Benjamin Moore Aura costs roughly twice a gallon of contractor-grade paint - but if it genuinely covers in one coat, you buy half as many gallons and save a full day of labor. Our cost panel shows the total side-by-side so you can see the real comparison.

Flat hides imperfections best - great for ceilings and low-traffic adult bedrooms. Eggshell is the most common choice for living rooms and bedrooms. Satin is washable without being shiny - good for kitchens, bathrooms, kids' rooms. Semi-gloss belongs on trim, doors, and cabinets. Gloss is reserved for high-wear accents and shows every flaw.

Real jobs lose paint to roller trays, overspray, dropped brushes, and the last quarter-inch stuck at the bottom of the can that you can't use. 10% is the professional standard. First-timers, complex rooms, or dark colors where a missed spot is obvious - use 15%.

Yes. Your inputs are saved to your browser automatically, and the 'Copy share link' button gives you a URL that encodes the full calculation so you can send it to a partner or pull it up on your phone at the store.

Most brand calculators either hide cost entirely or quote you their own premium line. We show three price tiers side-by-side using real national averages ($30 budget / $45 quality / $65 premium-one-coat), plus the primer, so you see honest total cost - not a push to buy their most expensive can.