Paint Calculator

Estimate how much paint you need from wall area, coats and coverage. Free, instant, no signup.

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Formula: Gallons = area × coats ÷ coverage per gallon

How to use the Paint Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the paint calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Paint Calculator

Instant results. Enter your figures and the paint calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

FREE
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  • Instant results
  • No signup
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About the Paint Calculator

The Paint Calculator turns your room measurements into a clear answer: how many gallons or quarts to buy for a job. You enter the wall dimensions (or total square footage), how many coats you plan to apply, and the number of doors and windows to subtract. The tool multiplies your paintable area by the number of coats, divides by a realistic coverage rate of about 350 square feet per gallon, and rounds up to a whole can. It exists to stop the two classic mistakes: buying three gallons for a job that needs one, or running short halfway through the second coat.

Reach for this before a hardware-store trip rather than guessing from the can label. Manufacturers print 400 square feet per gallon based on lab conditions, but real walls absorb more, especially bare drywall, patched spots, or rough textures. Two coats is the standard for true color and even hide, and a dramatic change (dark over light, or color over bare wall) usually wants a primer coat first. The calculator handles all of that so you can plan a single room, a whole apartment, or an exterior wall and know your shopping list before you leave the house.

Mechanically, it works from the painter's standard formula. It builds gross wall area from perimeter times height (or accepts your square footage directly), subtracts roughly 20 square feet per door and 10 square feet per window, multiplies by coats, then divides by the coverage rate. Primer is figured separately because it spreads thinner, around 200 to 300 square feet per gallon. Results round up because paint is sold in whole cans, and you genuinely want a little left over for touch-ups rather than a second trip mid-project.

Everything is computed in your browser the moment you submit. No measurements, room sizes, or project details are sent to a server, stored, or shared, so your numbers stay on your device. Treat the result as a tight estimate, not a guarantee: actual coverage shifts with surface porosity, paint sheen, application method, and how heavily you load the roller. When a calculation lands right on a boundary, the tool rounds up so you finish the job, and a leftover quart is far cheaper than an emergency run for one more can.

Frequently asked questions

How much area does one gallon of paint cover?

A gallon typically covers about 350 to 400 square feet of smooth, previously painted wall in one coat. This calculator uses roughly 350 square feet per gallon as a realistic working figure, since bare, porous, or textured surfaces absorb more and reduce real-world coverage.

How many coats should I plan for?

Two coats is the standard for walls to get even color and full hide. Painting the same color over itself can sometimes work in one coat, while a big color change or bare surface often needs a primer coat plus two finish coats.

How much do I subtract for doors and windows?

A common rule is about 20 square feet per door and 10 square feet per window. Those areas are not painted with wall paint, so subtracting them keeps you from over-buying, though you can fine-tune for unusually large openings.

Do I need separate primer, and how much?

Primer is recommended for bare drywall, big color changes, stains, or patchy repairs. It spreads thinner than paint, covering roughly 200 to 300 square feet per gallon, so estimate it separately rather than assuming the same amount as your finish coats.

Why does the calculator round up to whole cans?

Paint is sold in whole gallons and quarts, so the result rounds up to what you would actually buy. A small leftover amount is intentional and useful: it covers thin spots, drips, and future touch-ups without a second trip to the store.

From our blog

Healthy Weight by Height: How to Read and Use Your Range

By the Super Simple Digital Tools Team · Updated June 2026

Most people picture a single 'goal weight', but health authorities actually define a healthy weight as a span. The reason is simple: a person of a given height can carry slightly more or less weight, depending on frame and muscle, and still be perfectly healthy. The Healthy Weight Calculator captures this by giving you a low and a high figure that bracket the recognised healthy BMI zone of 18.5 to 24.9, turning an abstract index into something you can read off a scale.

The arithmetic behind it is the BMI formula run in reverse. BMI equals weight in kilograms divided by height in metres squared. To find the weights instead of the index, you fix BMI at the two boundary values and rearrange: lower weight equals 18.5 times height squared, upper weight equals 24.9 times height squared. A person 1.60 m tall has a height squared of 2.56, so their healthy band is roughly 47 kg to 64 kg. Add a few centimetres of height and the whole window shifts upward, which is exactly why a borrowed weight target from a taller friend rarely fits.

Once you have the range, the useful question is where you want to sit within it. Landing anywhere inside 18.5 to 24.9 is considered healthy, but many people aim for the middle of their band to leave room for the normal daily swings of one to two kilograms caused by water, food and timing. If your current weight is above the top of the range, the gap to the upper bound is a modest, achievable first goal rather than the daunting jump to the lowest figure. Small targets are easier to keep.

It is worth being clear about what the number cannot tell you. BMI was designed for population screening and treats all weight the same, so it cannot see whether your kilograms are muscle or fat. A rugby player and a sedentary person of identical height and weight get the same band, even though their health picture differs. That is why clinicians pair BMI with waist circumference, blood pressure and other checks. The calculator is a fast first filter, not a diagnosis.

To get the most reliable reading, measure your height accurately without shoes and weigh yourself at a consistent time, ideally in the morning. Re-check your range only if your height changes, which for adults is rare, and track your weight against the band over weeks rather than reacting to a single reading. Used this way, the healthy weight range becomes a steady reference point that supports gradual, sustainable change instead of crash targets.

  • Measure height in bare feet and weigh yourself at the same time of day for a like-for-like comparison against your range.
  • Aim for the middle of your band rather than the bottom edge, so normal daily fluctuations of one to two kilograms do not push you out of range.
  • If you are above the range, set the upper bound as your first milestone instead of the lowest figure, then reassess.
  • Pair the result with a waist measurement, since waist size adds information about fat distribution that BMI alone cannot capture.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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