Paint Needed Calculator – Know Exactly How Much Paint to Buy
Know how much paint you need before you open a single can.
✅ Free · No signup · No email required📊 Data from public industry sources🕐 Prices updated July 2026🔒 We never see your data🧑💻 Built by CoverWise · About us
Stop Guessing How Much Paint You Need
📊 Data sourced from publicly available industry standards. See our methodology page for formulas, sources, and limitations.
Nothing's worse than running out of paint halfway through a room, right?
Or worse—ending up with three extra gallons you'll never touch.
So I made this paint calculator for you. It tells you exactly how many gallons you need. No math. No guessing.
Most online calculators? Kinda useless. But this one actually works in square feet and meters. And it automatically subtracts your windows and doors.
Just punch in your room size, pick your paint type, and boom—you've got your number.
Here's the thing: most people overbuy by about 20%. That's like $30 to $60 down the drain on a typical bedroom. Use this calculator, and you'll grab exactly what you need. No waste.
How the Calculator Works
Here's the simple logic behind it. You tell us the width, length, and height of your room. The calculator figures out the total wall area. Then it subtracts a standard window (15 sq ft) and a standard door (21 sq ft). You can adjust those numbers if your windows are bigger or you have sliding doors.
Next, pick your paint type. Interior latex covers about 375 sq ft per gallon. Exterior latex is closer to 350. Primer covers around 325. The calculator uses these numbers to tell you exactly how many gallons you need.
Honestly, this won't work perfectly if your walls are heavily textured or if you're painting over dark colors. Those cases need more paint. But for standard walls, it's dead accurate.
Paint Coverage by Type
Different paints cover differently. Here's what to expect per gallon:
Why This Calculator Beats the Rest
Most paint calculators are stuck in the 1990s. They only work in square feet. They make you subtract windows and doors manually. Who has time for that?
This one does everything automatically. It handles metric too. You can switch between feet and meters with a click. No extra math, no conversion errors.
When I moved last year, I made this exact mistake. I used a basic calculator and ended up with 4 gallons of paint I never touched. That's $140 down the drain. Don't be me. Use the right tool.
How Many Gallons for a Typical Room?
A standard 12x15 bedroom with 8.5-foot ceilings needs about 2 gallons of interior latex for one coat. That's with one window and one door subtracted. If you're doing two coats, double it to 4 gallons.
A larger 15x20 living room with the same ceiling height needs around 3 gallons per coat. Primer for new drywall? You'll need about 3.5 gallons for that same room.
Use the calculator above to get your exact number. Every room is different.
Paint Prices and Budgeting
Paint prices vary wildly. Cheap stuff runs $15 a gallon. Premium brands like Sherwin-Williams or Behr can hit $70. Most people spend around $35 per gallon for decent quality.
For a typical bedroom needing 2 gallons per coat, you're looking at $70 for one coat or $140 for two. That's paint only. Add brushes, tape, and drop cloths, and budget another $30 to $50.
If you're painting a whole house, those numbers add up fast. Our calculator helps you budget accurately before you step foot in the store.
Tips for Accurate Measurement
Measure your room at the baseboard. Don't measure at the ceiling—ceilings can be uneven. Use a steel tape measure, not a cloth one. Cloth tapes stretch over time.
Measure width and length in two spots each. Take the average if they're different. Old houses are rarely perfectly square.
For ceiling height, measure from floor to ceiling in the center of the room. Corners can be higher or lower by an inch or two.
CoverWise Pick•Our Recommendation
CoverWise Pick: Sherwin-Williams SuperPaint Interior Latex
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Frequently Asked Questions
- How many square feet does a gallon of paint cover?
- Interior latex covers 350 to 400 sq ft per gallon. Exterior latex covers 300 to 400. Primer covers 300 to 350.
- Does the calculator subtract windows and doors automatically?
- Yes. It subtracts a standard window (15 sq ft) and a standard door (21 sq ft). You can adjust these numbers if needed.
- Can I use this calculator in meters?
- Yes. Switch to metric mode and enter your dimensions in meters. The calculator handles the conversion automatically.
- How many gallons for a 12x12 room?
- Use the calculator. For a 12x12 room with 8-foot ceilings and one window and door, you'll need about 1.5 gallons per coat.
- What if my walls are textured?
- Textured walls absorb more paint. Add 10 to 20% to the calculator's estimate. A good rule: buy one extra gallon for every 4 gallons recommended.
- Should I buy extra paint for touch-ups?
- In my experience, yes. Buy 1 extra quart for small touch-ups. It's better than trying to match the color later.
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