Paint Calculator: How Much Paint Do You Need?

Ever stood in the paint aisle, staring at a row of gallons, wondering how much you really need? That’s where a paint calculator makes things easier.

No overbuying or running out halfway through a wall. Just clear numbers based on your actual room size and layout.

Whether you’re repainting a bathroom or refreshing the living room, this tool gives you a more accurate estimate. It’s especially helpful if you’re managing a budget or working within a tight schedule. If you’re applying more than one coat or tackling both walls and ceiling, it does the math for that too.

This guide breaks it all down in plain language, so using a paint calculator feels a little less confusing and a lot more helpful.

Key Takeaways:

• A paint calculator helps prevent overbuying or running out mid-project.
• Enter room size, wall height, and number of coats for a fast paint estimate.
• It subtracts windows and doors to give you an accurate surface area.
• Ceiling painting and custom room shapes are included in the calculator.
• Ideal for painting projects, saving time and money.

How the Paint Calculator Works

The paint calculator looks at the total surface area you want to paint and subtracts areas you don’t. It gives you an estimate of how many gallons (or quarts) you’ll need based on standard paint coverage. Most interior paint covers about 350 square feet per gallon. If you need two coats or you’re using primer, that number doubles.

To get an accurate number, you’ll enter room dimensions, ceiling info, how many windows or doors, and how many coats you plan to apply.

The tool works for all kinds of surfaces, whether you’re working with drywall, concrete, or wood. You can use it for interior projects like a bedroom, kitchen, or bathroom, or even for exterior painting like a garage wall or brick siding.

Getting Started: Measuring Your Space

You’ll need a few basic measurements to start:

• Wall width and height (in feet or inches)
• Number of walls
• Window and door count
• If you want to paint the ceiling
• How many coats of paint

Once that’s in, the calculator takes care of the rest.

Understanding the Inputs

Room Shape

Choose your layout. Most people go with either rectangle, square, or custom. The shape affects how the square footage is calculated. A square room is easy math, but custom shapes may need more wall entries.

If you’re dealing with an open floor plan or a weirdly angled space, the custom option lets you plug in each wall one by one. You’ll just need the length and height of each.

Wall Dimensions

This is the core of the calculation. For each wall, enter the width and height. The calculator will multiply them to get the total square feet. If you’re doing multiple walls (like an entire room), you can add more as needed.

If you’re painting a kitchen, you might skip areas covered by cabinets or appliances. Same goes for a bathroom if much of the wall is tile or glass. For those situations, subtracting footage using window and door inputs will help adjust the total.

Windows and Doors

Every window and door takes up wall space you’re not painting. A standard door is about 20 square feet and a window is around 15. The paint calculator subtracts this from your wall total automatically. Just count how many you have and enter the numbers.

If your home has large glass sliding doors or oversized windows, you might want to adjust the area manually.

Ceiling Paint

The calculator will include it once you check that option. You’ll need to add the length and width of the room to get the ceiling’s square footage. This is especially helpful for spaces like a bedroom, where the ceiling gets the same color or finish.

If you’re painting a textured ceiling or covering up a darker interior paint, plan for more paint. You’ll probably want to factor in two coats and maybe even a good primer to help with adhesion.

Number of Coats

The tool defaults to two coats, which is pretty standard. That gives you better coverage and durability. But if you’re applying a fresh color over a similar shade, one might be enough.

On the flip side, going from dark to light? You might need a third coat or a primer underneath. We talk more about that in our blog on coats of primer if you want a deeper breakdown.

A Quick Example

Let’s say you’re painting a 12×12 bedroom with 8-foot ceilings, two windows, and one door. You’re painting the walls only and using two coats.

• Wall area: 384 square feet
• Subtract 50 square feet for the windows and door
• That leaves 334 square feet
• At 350 square feet per gallon, you’ll need just under one gallon for one coat
• Two coats? You’ll want 2 gallons to be safe

That same math applies to larger spaces like a living room, kitchen, or interior office.

If you’re changing the paint sheen, like switching from matte to satin, check out our paint sheen guide before you start. That plays a role in coverage too.

Why a Paint Calculator Makes a Difference

There’s nothing worse than being halfway through a wall and realizing you’re out of paint. Or buying too much and ending up with a few half-used gallons sitting in the garage.

The paint calculator gives you a more accurate estimate, especially when you factor in things like ceilings, wood trim, or painting over wood stain. It’s perfect for home improvement projects where budget, time, and mess all matter.

Final Thoughts

The paint calculator takes the guesswork out of planning your next painting project. Whether you’re painting a single room or the whole house, it gives you a solid starting point. Just grab a tape measure, plug in your dimensions, and let the numbers do the rest.

It’s straightforward, quick to use, and saves you time on the back end trying to return unused cans or rushing to the store mid-project.

Here’s how Norse Painting makes it easier:

• We offer free estimates and help calculate exact square footage
• We’ll help you choose the right paint, primer, and color for your space
• Our team handles everything from pressure washing to prep and cleanup
• You get certified painters, high-quality products, and attention to detail
• We paint interiors, exteriors, kitchens, bathrooms, and more—no corner skipped

Let Norse Painting bring your vision to life. If you’re in Las Vegas, Henderson, North Las Vegas, NV and the surrounding areas, call us at 725-217-5377 for a FREE estimate.