Paint Calculator Benjamin Moore: How Much You Need

This paint calculator works out how many gallons of Benjamin Moore paint you need for a room, based on the wall area you enter and the number of coats you plan to apply. You input the total square footage to be painted and the number of coats, and it returns the required gallons (rounded up to the nearest whole gallon, since paint is sold by the gallon). It also shows the raw square footage coverage so you can see the math behind the result.

Formula

The standard rule for Benjamin Moore (and most architectural paints) is that one gallon covers approximately 350 square feet with a single coat. The formula is:

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

• Wall Area – the total surface you plan to paint, in square feet (include windows and doors only if you will paint them; otherwise subtract them).
• Number of Coats – usually 2 for a color change, 1 for a same-color touch-up, or 3 for a dramatic shift (e.g., dark to light).
• 350 – the approximate coverage of one gallon of Benjamin Moore paint on a smooth, primed surface (sq ft per gallon).
• ceil() – rounds up to the next whole number, because you cannot buy a fraction of a gallon.

This formula is the same one used by professional painters and Benjamin Moore’s own project calculators. It assumes a properly prepared surface and a standard roller or brush application.

Worked Example

Using the default inputs: wall area = 400 sq ft, coats = 2.

1. Total coverage needed = 400 × 2 = 800 sq ft.
2. Divide by coverage per gallon: 800 ÷ 350 = 2.2857…
3. Round up to the nearest whole gallon: 3 gallons.

So for a 400 sq ft room with two coats, you need 3 gallons of Benjamin Moore paint. The calculator shows the coverage needed (800 sq ft) as a secondary output.

How to Measure Your Room

To get an accurate number, you need the total square footage of the surfaces you will paint. For walls:

• Measure the length of each wall and the ceiling height (in feet).
• Multiply length × height for each wall, then add them together.
• Subtract the area of windows and doors (about 15–20 sq ft per standard window, 20 sq ft per door) if you are not painting those.
• For ceilings, measure length × width of the room.

If you are painting trim, baseboards, or cabinets, measure those separately – they use less paint per square foot but still count. This calculator is for walls and ceilings; for trim, a quart is often enough for a typical room.

Common Mistakes and Misconceptions

The biggest mistake is forgetting to subtract windows and doors. A 12×12 room with two windows and a door might have about 400 sq ft of wall area, but if you measure the full wall surface without subtracting, you could overestimate by 10–15%. Another common error is using the wrong coverage number. Benjamin Moore’s premium paints (like Regal Select or Aura) list coverage at 350–400 sq ft per gallon, but this is for a smooth, primed surface. If your walls are rough, unpainted drywall, or heavily textured, coverage drops to 250–300 sq ft per gallon – in that case, adjust the formula by using 300 instead of 350.

A frequent misconception: “I only need one coat because the paint is high quality.� In reality, even premium paint often needs two coats for even color, especially when going from a dark to a light shade. The calculator’s default of 2 coats is the safe choice.

How Many Coats Do You Really Need?

The number of coats depends on the color change and surface condition:

• 1 coat – repainting the same color, touching up, or applying paint over a perfectly matched primer.
• 2 coats – standard for most projects: new drywall (after primer), light-to-medium color changes, or painting over white.
• 3 coats – going from a very dark color to a very light one, or covering a bold red/orange. Sometimes a tinted primer reduces this to 2 coats.

If you are unsure, buy enough for 2 coats. You can always return unopened gallons, but running out mid-project is frustrating.

What About Primer?

Primer is a separate product and is not included in this calculator. For bare drywall, stained walls, or drastic color changes, you should use a Benjamin Moore primer first – usually 1 coat, and it covers about 300–400 sq ft per gallon. If you are priming, add that to your total: for a 400 sq ft room, you would need 1 gallon of primer (400 ÷ 350 ≈ 1.14, round up to 2? No, 1 gallon covers 400 sq ft at 350, so you need 1.14 → 2 gallons if you round up, but actually 1 gallon covers 400 sq ft exactly at 350, so 1 gallon is enough for one coat; but to be safe, buy 1 gallon). Many painters skip primer when repainting the same color, but for new surfaces it is essential.

Cost Considerations

Benjamin Moore paints are premium priced – a gallon typically costs more than budget brands. The calculator tells you how many gallons, so you can multiply by the price per gallon at your local retailer. For a 400 sq ft room with 2 coats (3 gallons), you might spend roughly $150–$250 depending on the line (Aura is pricier than Regal Select). Buying the exact number of gallons avoids waste, but remember that most stores accept returns of unopened cans.

Frequently Asked Questions

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

A 12×12 room with 8-foot ceilings has about 384 sq ft of wall area (4 walls × 12 ft × 8 ft = 384), minus a door and window (say 40 sq ft) = 344 sq ft. For 2 coats, you need 344 × 2 = 688 sq ft, divided by 350 = 1.97, so you need 2 gallons. If you also paint the ceiling (144 sq ft), add 1 more gallon for 2 coats.

Is one gallon of Benjamin Moore enough for one wall?

Yes, typically. A single wall in a standard room is about 100–150 sq ft, so one gallon (350 sq ft) covers it with 2 coats easily. For a large accent wall (e.g., 12 ft × 10 ft = 120 sq ft), one gallon is enough for 2 coats.

Does Benjamin Moore’s Aura cover more than Regal Select?

Both are rated at about 350–400 sq ft per gallon, but Aura is a thicker, higher-solids paint that may provide better one-coat coverage in some colors. However, for most projects, plan on 2 coats with either. The coverage difference is minimal, so use the same 350 sq ft per gallon in the calculator.

How do I calculate paint for a room with vaulted ceilings?

Measure the height at the tallest point and the width of each wall section separately, then calculate each triangular or trapezoidal area. Add those to the rectangular wall areas. The formula remains the same – total sq ft × coats ÷ 350. Vaulted ceilings increase area, so you will need more gallons.

Can I return unopened paint to Benjamin Moore?

Most Benjamin Moore retailers accept returns of unopened, non-tinted paint within 30 days, but tinted paint is usually non-returnable. To avoid waste, buy the calculated number of gallons and keep the receipt. If you are unsure, buy one extra gallon only if you are near the end of a project and cannot get more later.

Why does the calculator round up to the nearest gallon?

Paint is sold in whole gallons (and quarts). You cannot buy 2.3 gallons, so rounding up ensures you have enough. If the result is 2.1, you need 3 gallons. This is the standard practice in the industry.

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in area | Wall area to paint | sq ft | 400 | 0
in coats | Number of coats | - | 2 | 1
out gallons | Paint needed | gallons | ceil(area * coats / 350) | 0
out coverage | Total coverage needed | sq ft | area * coats | 0