Paint Calculator: Exact Material Lists for Pros & DIYers
Paint Calculator: Exact Material Lists for Pros & DIYers
There is nothing worse than finishing 95% of a room and running out of paint. You have to drive back to the store, and the new can might have a slightly different color lot, ruining the finish.
On the flip side, buying 5 gallons when you only needed 3 is a $150 mistake. This professional tool by ShockTrail solves the math so you can focus on the finish.
The Room Estimator
Calculate paint and primer requirements based on dimensions, texture, and coats.
Room Paint Estimator
Professional Coverage CalculatorWall Paint
0 GallonsNet Wall Area: 0 sq ft.
Coverage Rate Used: 0 sq ft/gal.
*Always buy a little extra for touch-ups.
PART 1: The Science of Coverage (Spread Rate)
Paint manufacturers like Sherwin Williams, Benjamin Moore, and Behr usually state that one gallon covers 350 to 400 square feet. However, this number assumes a perfectly smooth, primed, non-porous wall applied by a professional with a roller.
Variables That Kill Your Coverage
In the real world, “400 sq ft per gallon” is a myth. Here is why:
- Texture: Popcorn ceilings, orange peel, or knock-down textures increase surface area by 20-50%.
- Application Method: An airless sprayer is faster but wastes 20-30% of paint due to overspray and line purging.
- Color Change: Going from dark red to light gray? You will need 3 coats, not 2.
- Drywall Thirst: Fresh drywall (new construction) acts like a sponge. The first coat (primer) disappears almost instantly.
PART 2: Real-World Case Studies
Understanding the math is easier when we look at actual projects. Here are three scenarios analyzed by ShockTrail renovation experts.
Case Study 1: The Standard Master Bedroom
The Project: A 12ft x 15ft bedroom with 8ft ceilings. It has 1 door and 2 windows. The walls are smooth, currently painted white, and will be repainted light blue.
The Math:
- Perimeter: (12+12+15+15) = 54 linear feet.
- Gross Wall Area: 54′ × 8′ = 432 sq ft.
- Subtractions: Door (20 sq ft) + 2 Windows (15+15 = 30 sq ft) = -50 sq ft.
- Net Area: 382 sq ft.
The Result: Since coverage is ~350 sq ft/gallon:
- 1 Coat: ~1.1 gallons.
- 2 Coats (Standard): ~2.2 gallons.
Buying Decision: The homeowner must buy 3 Gallons. Alternatively, buy a 5-gallon bucket to save money if painting the closet too.
Case Study 2: The Open-Concept Living Room (High Ceilings)
The Project: A large living area (20ft x 25ft) with vaulted 12-foot ceilings. The walls have “Orange Peel” texture. Application will be done with a roller.
The Math:
- Perimeter: 90 linear feet.
- Gross Area: 90′ × 12′ = 1,080 sq ft.
- Subtractions: Large patio doors and windows (~100 sq ft).
- Net Area: 980 sq ft.
The Texture Factor: Orange peel texture reduces coverage to ~300 sq ft/gallon.
980 sq ft ÷ 300 = 3.26 gallons per coat.
The Result: For 2 coats, you need 6.5 gallons.
Buying Decision: Order Two 5-Gallon Buckets (10 gals). Why? Because running out on a 12-foot ladder is dangerous and frustrating. The extra paint is worth the peace of mind.
Case Study 3: The Exterior Stucco House
The Project: Repainting the exterior of a small 40ft x 30ft house. The surface is rough Stucco. Method: Airless Sprayer.
The Math:
- Perimeter: 140 linear feet.
- Height: 10ft. Area: 1,400 sq ft.
- Subtractions: ~150 sq ft (windows/doors). Net: 1,250 sq ft.
The “Stucco + Spray” Factor: Stucco is thirsty (reduces coverage to 200 sq ft/gal). Spraying wastes 20%.
- Effective coverage: ~160 sq ft/gallon.
- 1 Coat: 1,250 / 160 = 7.8 gallons.
- 2 Coats: 15.6 gallons.
Buying Decision: Buy Three 5-Gallon Buckets (15 gals) and one single gallon. Or just round up to 20 gallons to be safe.
PART 3: To Prime or Not to Prime?
Primer is cheaper than paint ($20 vs $60). Skipping primer is the most expensive mistake you can make because you will end up using 3-4 coats of expensive paint to get coverage.
When Primer is MANDATORY:
- New Drywall: The paper and mud compound absorb moisture differently. Without PVA primer, your finish coat will look “blotchy” (flashing).
- Drastic Color Change: Going from Black to White? Use a high-hiding primer. Going from White to Red? Use a grey-tinted primer to help the red cover better.
- Stains/Odors: If the wall has water damage, crayon marks, or smoke damage (cigarettes), you need an oil-based or shellac primer (like Kilz or BIN) to block the bleed-through.
- Glossy Surfaces: Paint does not stick to glossy oil paint or varnish. You need a bonding primer.
Pro Tip: “Paint and Primer in One” is a marketing term. It is fine for repainting similar colors, but it is NOT a substitute for real primer on raw surfaces.
PART 4: Sheen Guide – Gloss vs. Matte
The “Sheen” determines how shiny the wall is. It affects durability and how well it hides mistakes.
| Sheen Level | Reflectivity | Best Use Case |
|---|---|---|
| Flat / Matte | 0-5% (No Shine) | Ceilings and low-traffic areas. Hides imperfections perfectly but is hard to clean. |
| Eggshell / Satin | 10-25% (Low Luster) | Living Rooms & Bedrooms. The standard choice. Washable but doesn’t glare. |
| Semi-Gloss | 35-60% (Shiny) | Trim, Doors, Kitchens, Bathrooms. Very moisture resistant and easy to scrub. |
| High Gloss | 70%+ (Mirror-like) | Cabinets & Furniture. Ultra durable but highlights every scratch or dent. |
PART 5: Application Methods (Roller vs. Sprayer)
Should you roll or spray? Here is the breakdown from ShockTrail.
Rolling (The Reliable Way)
Pros: No complex masking required. Thick, even coat. Good adhesion.
Cons: Slow. Physically tiring.
Coverage: ~350-400 sq ft/gal.
Spraying (Airless)
Pros: Extremely fast (paint a whole house in a day). Glass-smooth finish on doors/trim.
Cons: Requires massive prep work (masking everything). Wastes paint.
Coverage: ~250-300 sq ft/gal (due to waste).
Warning: Never stop moving your hand when the trigger is pulled, or you will get runs.
PART 6: Preparation is 80% of the Job
The difference between a DIY job and a Pro job is not the painting; it is the prep.
- Wash Walls: Use TSP (Trisodium Phosphate) to remove grease, especially in kitchens.
- Patch Holes: Use spackle for small holes. Sand it smooth. Prime the patch before painting, or the patch will absorb paint differently and show up as a dull spot (flashing).
- Caulk Trim: Run a bead of paintable caulk along baseboards and crown molding for a seamless look.
- Tape: Use high-quality tape (FrogTape) and remove it while the paint is still slightly wet to prevent peeling.
Frequently Asked Questions (FAQ)
How many square feet does a 5-gallon bucket cover?
Typically 1,750 to 2,000 square feet for one coat on smooth walls. For textured walls, expect 1,250 to 1,500 square feet.
Do I really need 2 coats?
Yes. The first coat provides coverage; the second coat provides the true color depth, sheen uniformity, and durability. Single-coat applications often look streaky in varied lighting.
How do I calculate for the ceiling?
Ceiling area is simply Length × Width. Ceilings usually soak up more paint because they are flat sheen and often textured (popcorn). Always buy separate “Ceiling Paint” which is formulated to drip less.
Relevant Search Tags
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