Paint Calculator Interior Benjamin Moore

This paint calculator helps you estimate how many gallons of Benjamin Moore interior paint you need for a room or whole house. You enter the room’s dimensions, the number of doors and windows, and how many coats you plan to apply; it returns the total wall area in square feet and the gallons required. The calculator uses the standard coverage rate of 350 square feet per gallon for Benjamin Moore interior paints, which is the rate the company lists for most of its wall paints.

Formula

The calculator uses two simple formulas. First, find the total paintable wall area:

Wall Area = (2 × L × H) + (2 × W × H) − (D × 21) − (Win × 12)

Where:

• L = room length (feet)
• W = room width (feet)
• H = wall height (feet)
• D = number of standard interior doors (each subtracts 21 sq ft)
• Win = number of standard windows (each subtracts 12 sq ft)

Then convert to gallons:

Gallons = (Wall Area × Number of Coats) / 350

The 350 square feet per gallon is the typical coverage for Benjamin Moore interior latex paints when applied with a roller at the recommended film thickness. Coverage can vary with surface porosity, application method, and color change, so treat the result as an estimate, not a guarantee.

Worked Example

Using the calculator’s default values: a 12 ft × 10 ft room with 8 ft ceilings, 2 doors, 2 windows, and 2 coats.

1. Calculate the perimeter walls: (2 × 12 × 8) + (2 × 10 × 8) = 192 + 160 = 352 sq ft.
2. Subtract openings: 2 doors × 21 = 42; 2 windows × 12 = 24. 352 − 42 − 24 = 286 sq ft.
3. Multiply by coats: 286 × 2 = 572 sq ft.
4. Divide by coverage: 572 / 350 = 1.63 gallons.

The calculator rounds to 1.6 gallons. Since paint is sold in full gallons, you would need to buy 2 gallons for this project. If you were painting the ceiling too, add the ceiling area (length × width = 120 sq ft) and adjust accordingly.

Why Benjamin Moore Coverage Differs

Benjamin Moore’s interior paint lines—like Regal Select, Aura, and ben—all list a coverage of 350–400 sq ft per gallon. The exact number depends on the sheen and the specific product. Flat and matte finishes tend to cover slightly better because they have more pigment and less binder. Eggshell and satin are close behind. High-gloss paints cover less because they leave a thinner film; you might get only 300–350 sq ft per gallon. If you are using a primer, note that primer typically covers 300–400 sq ft per gallon, so you may need a separate calculation for the primer coat.

How to Measure a Room for Painting

Accurate measurements are the foundation of a good estimate. Follow these steps:

• Measure the length and width of the room in feet, from wall to wall, not including baseboards.
• Measure the wall height from the floor to the ceiling. If the ceiling is sloped or has a tray, measure the tallest point and the shortest point and average them.
• Count the number of doors and windows. For non-standard sizes, measure the actual height and width of each opening and subtract that area.
• Decide how many coats you need. One coat is rarely enough for a color change; two coats are standard for most repaints. If you are painting over a dark color with a light one, or over bare drywall, you may need three coats or a primer first.

For a quick manual check, you can also use the “perimeter × height� method: add the lengths of all walls, multiply by the height, then subtract openings. That works for rooms with more than four walls, like L-shaped spaces.

Common Mistakes and How to Avoid Them

One of the most frequent errors is forgetting to subtract door and window areas. A standard interior door is about 21 sq ft, and a typical window is about 12 sq ft. In a 12×10 room, those openings reduce the area by 66 sq ft—about 19% of the wall area. Skipping that step can lead you to buy an extra gallon.

Another common mistake is mixing units. If you measure in inches, convert to feet first (divide by 12). The calculator expects feet. If you measure in meters, convert to feet (multiply by 3.281) or use a metric paint calculator. Also, be consistent: if you measure the room in feet, measure the doors and windows in feet too.

Rounding too early can also cause problems. If you calculate 1.63 gallons and round down to 1.5, you might be short. Always round up to the nearest full gallon when buying. Paint stores do not sell half gallons in most interior lines, so you will buy 2 gallons even if you only need 1.6.

How to Read the Result

The calculator gives you two numbers: total wall area and gallons needed. The gallons figure assumes you buy whole gallons. For example, 1.6 gallons means you need 2 gallons. If the result is 2.1, you need 3 gallons. It is always better to have a little extra paint for touch-ups than to run out mid-project.

If you are painting multiple rooms, run the calculation for each room separately and add the totals. This is more accurate than estimating a whole house at once, because rooms have different numbers of doors and windows.

Limitations of the Formula

The 350 sq ft per gallon rate is an ideal number. Real-world coverage can be lower for several reasons:

• Porosity: Bare drywall, plaster, or unpainted wood soaks up more paint. A primer coat is recommended for these surfaces.
• Color change: Going from a dark color to a light one, or vice versa, often requires an extra coat.
• Application method: Sprayers use more paint than rollers; thick-nap rollers use more than thin-nap.
• Texture: Textured walls (popcorn, knockdown) have more surface area and need more paint.
• Temperature and humidity: Painting in very hot or dry conditions can cause the paint to dry faster and reduce coverage.

If you are painting a ceiling, add the ceiling area separately. Ceilings usually need one coat of primer and one coat of paint, but if you are covering stains, you may need a stain-blocking primer first.

Frequently Asked Questions

How much paint do I need for a 12×12 room?

For a 12×12 room with 8-foot ceilings, two doors, and two windows, the wall area is (2×12×8)+(2×12×8) = 384 sq ft, minus 66 sq ft for openings = 318 sq ft. For two coats, that’s 636 sq ft. At 350 sq ft per gallon, you need 1.8 gallons, so buy 2 gallons. If you are also painting the ceiling, add 144 sq ft, bringing the total to 780 sq ft, which is 2.2 gallons—so 3 gallons for the whole room.

Does Benjamin Moore paint really cover 400 sq ft per gallon?

Some Benjamin Moore products, like Aura, list 400 sq ft per gallon on smooth, primed surfaces. However, most painters find that 350 sq ft per gallon is a more realistic average for interior walls, especially when applying two coats. The lower estimate is safer for budgeting.

Should I use a primer with Benjamin Moore paint?

Primer is recommended for bare drywall, new wood, or when making a dramatic color change. Benjamin Moore makes specific primers like Fresh Start, which is designed to seal and provide a uniform base. Using primer can reduce the number of topcoats you need, so it often saves money overall.

How many coats of Benjamin Moore paint should I use?

Two coats is the standard for most interior repaints. One coat may be enough if you are painting the same color with a similar sheen, but it rarely looks as even or durable. For deep or vibrant colors, three coats might be necessary to achieve full opacity.

What if my walls are textured?

Textured walls have more surface area than smooth walls, so coverage drops. Add 10–20% more paint to your estimate. For heavy textures like popcorn, you might need 30% more. The calculator’s result is for smooth walls, so adjust upward for texture.

Can I use this calculator for Benjamin Moore exterior paint?

No, exterior paint has different coverage rates and considerations. Exterior surfaces are often more porous and rough, and you may be painting siding, brick, or stucco. Use a dedicated exterior paint calculator for those projects.

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in a | Room length | ft | 12 | 0
in b | Room width | ft | 10 | 0
in h | Wall height | ft | 8 | 0
in d | Number of doors | - | 2 | 0
in w | Number of windows | - | 2 | 0
in c | Coats | - | 2 | 1
out area | Total wall area | sq ft | (2*a*h + 2*b*h) - (d*21 + w*12) | 0
out gal | Gallons needed | gal | (area * c) / 350 | 1