Construction Calculators
Jump to a tool or explore below.
Paint Calculator
Estimate how much paint you need for interior and exterior projects. Calculate gallons, coverage, coats, and total cost instantly.
Room Paint Calculator
Calculate paint requirements for walls, ceilings, and multiple coats
How to Calculate Paint
Everything you need to know about estimating paint for your next project
Coverage Rates by Paint Type
- Standard Wall Paint:Covers approximately 350 sq ft per gallon on smooth, primed surfaces
- Ceiling Paint:Covers approximately 400 sq ft per gallon due to thicker, drip-resistant formula
- Primer:Covers approximately 300 sq ft per gallon and is essential for bare surfaces or color changes
- Textured Surfaces:Covers only 200 sq ft per gallon on stucco, brick, or heavily textured walls
Choosing the Right Paint
- Flat / Matte:Best for ceilings and low-traffic rooms; hides imperfections well
- Eggshell:Popular for living rooms and bedrooms; slight sheen with good washability
- Satin:Ideal for kitchens, bathrooms, and hallways; durable and moisture-resistant
- Semi-Gloss:Great for trim, doors, and cabinets; highly durable and easy to clean
- High-Gloss:Best for accents and high-traffic areas; most durable but shows imperfections
Surface Preparation
- 1Clean walls with a damp cloth or TSP solution to remove dust and grease
- 2Fill holes and cracks with spackle, then sand smooth once dry
- 3Apply painter's tape along trim, ceilings, and edges for clean lines
- 4Prime bare drywall, repaired areas, or when making drastic color changes
- 5Lightly sand glossy surfaces so the new paint adheres properly
Pro Tips for Painting
- Buy Extra:Purchase 10-15% more paint than calculated to account for touch-ups and waste
- Two Coats Minimum:Always plan for at least two coats for even coverage and true color
- Use Primer Separately:A dedicated primer coat is more effective than paint-and-primer-in-one products
- Paint in Order:Start with the ceiling, then walls, then trim and doors for the cleanest results
- Temperature Matters:Paint between 50-85F (10-30C) and avoid high humidity for best adhesion and drying
How to Calculate Paint for a Room: Step by Step
Walk through a real example to see exactly how to estimate paint for a typical room.
Example: 12 x 14 Room with 9-Foot Ceilings
Step 1: Calculate total wall area
Perimeter = 2 × (12 + 14) = 52 linear feet
Step 2: Subtract doors and windows
Assume 1 door (21 sq ft) and 2 windows (2 × 15 = 30 sq ft):
Step 3: Divide by coverage rate
Standard interior latex covers ~375 sq ft per gallon:
Step 4: Multiply by number of coats
Two coats are recommended for even coverage:
Step 5: Estimate cost
At $35 per gallon for mid-range interior paint:
Add $15-25 for tape, rollers, and brushes if you don't already have supplies.
Paint Calculator FAQ
How much paint do I need for a 12x12 room?
About 1.5 gallons for walls only (384 sq ft of wall area minus doors/windows, at 350-400 sq ft/gallon coverage). Two coats doubles this to ~3 gallons.
How many square feet does a gallon of paint cover?
Most interior latex paints cover 350-400 square feet per gallon on smooth surfaces. Textured or porous surfaces reduce coverage to 250-300 sq ft/gallon.
How much does it cost to paint a room?
DIY: $50-100 for a 12x12 room (2-3 gallons of mid-range paint). Professional: $300-800 depending on room size, prep work, and ceiling height.
Do I need primer before painting?
Yes for new drywall, dark-to-light color changes, stained surfaces, and bare wood. Not needed when repainting similar colors with paint-and-primer products.
How many coats of paint do I need?
Two coats for best coverage and durability. One coat may suffice for touch-ups with the same color. Dark colors over light may need 3 coats.
What is the difference between flat, eggshell, and satin paint?
Flat: no sheen, hides imperfections, hard to clean (ceilings, low-traffic). Eggshell: slight sheen, washable (living rooms, bedrooms). Satin: noticeable sheen, very washable (kitchens, bathrooms, trim).
Need Material Takeoff Tools?
BuildVision AI automatically calculates material quantities from your plans, including paint, finishes, and surface area requirements.
How the Paint Calculator Works
A 12 x 14 bedroom with 8-foot ceilings is 416 square feet of wall. Subtract one door (20 SF) and two windows (30 SF) and you are at 366 SF — two coats is 732 SF, which at 350 SF per gallon is 2.1 gallons, not the "gallon per room" a lot of crews still order by. Put that room on unprimed drywall drinking its first coat at closer to 275 SF per gallon and the shortfall gets worse. Multiply the miss across a 20-unit repaint and the paint order is off by cases, not quarts.
Painting subs use this to build material counts for repaint and new-construction bids; GCs use it to sanity-check a painter's quote before it goes into the estimate; production builders use it to standardize per-unit paint orders across a plan set. The discipline that matters is measuring walls, ceilings, and trim as three separate line items — they take different products at different coverage rates and different labor productivity, and a single blended square-foot number hides all of it.
Paint quantity math
- Wall area = room perimeter x ceiling height
- Paintable area = wall area - (doors x 20 SF) - (windows x 15 SF)
- Gallons = (paintable area x coats) / coverage per gallon
- Coverage per gallon = 400 SF smooth, 300-350 SF light texture, 250-300 SF heavy texture or bare drywall
- Ceiling gallons = (length x width x coats) / coverage per gallon
Estimating Steps and Checks
Measure walls, ceilings, and trim as separate line items
Walls get wall paint, ceilings get flat ceiling paint, and trim gets enamel — three products, three coverage rates, three labor rates. Perimeter times ceiling height for walls, length times width for ceilings, and linear feet for base, casing, and crown. Lumping them into one number is how trim enamel ends up missing from the order.
Subtract openings honestly — then decide if you should
The standard deductions are 20 SF per door and 15 SF per average window. On a room with one door and one window, many painters skip the deduction and let it ride as a built-in waste and touch-up factor — reasonable. On a wall of storefront glass, a garage door, or a slider, always deduct, or the count balloons.
Pick a coverage rate that matches the surface, not the label
The 400 SF per gallon on the can assumes a smooth, sealed, previously painted wall. Orange peel and light knockdown pull it to 300-350; heavy texture, bare drywall, and patched surfaces to 250-300; raw masonry and stucco can drink the first coat at well under 250. When in doubt, price the lower rate — the extra gallon is cheaper than a second trip.
Set coats and primer from the substrate and the color change
New drywall gets a PVA primer coat plus two finish coats — no exceptions if you want uniform sheen. A deep color change (dark to light, or into saturated reds and blues) gets a tinted primer plus two coats. A same-color, same-sheen repaint in good condition may cover in one, but bid two: the one-coat jobs that actually cover in one are rarer than the ones that don't.
Common Checks
- Coverage cheat sheet: smooth previously painted walls 350-400 SF per gallon, light texture 300-350, heavy texture and bare drywall 250-300, raw masonry or stucco can run below 250 on the first coat and recover on the second.
- Round up to whole gallons per color and per sheen — you cannot combine a wall gallon and a trim quart into one SKU — and once a single color passes about 4 gallons, order a 5-gallon bucket for batch consistency and leave the remainder labeled on site for punch-list touch-up.
- Spot-priming patches with wall paint instead of primer causes flashing — dull spots that telegraph through the finish coat, especially in eggshell and satin. Prime every patch, or plan on a full extra coat to bury them.
- Watch the application method: spraying goes on fast but can use 20 to 30 percent more material than rolling once overspray is counted, so a sprayed job needs its own waste factor even though the wall area is identical.
Paint Calculator FAQs
How much paint do I need for a 12x12 room?
With 8-foot ceilings, a 12 x 12 room is 48 feet of perimeter times 8, or 384 SF of wall. Subtract a door (20 SF) and a window (15 SF) to get 349 SF; two coats is 698 SF, which at 350 SF per gallon is right at 2 gallons. The ceiling is another 144 SF — figure about half a gallon per coat in ceiling paint, ordered separately.
How many square feet does a gallon of paint cover?
Plan on 250 to 400 SF per gallon depending on texture and porosity. The 400 number on the can assumes smooth, sealed, previously painted walls; light texture drops it to 300-350, and heavy texture, bare drywall, or masonry drops it to 250-300 or below on the first coat. Estimating at 350 for typical repaint work and 275 for unprimed or textured surfaces keeps you out of trouble.
Do I really need two coats of paint?
For any color change, sheen change, or new drywall, yes — one coat will show roller marks, flashing, and the old color reading through. The only realistic one-coat scenario is a same-color, same-sheen refresh on walls in good condition, and even then most painters bid two coats and treat a one-coat outcome as margin. Two-coat math is simple: double the paintable area before dividing by coverage.
When do I need primer before painting?
Four cases: new drywall (PVA primer, always), a dramatic color change (tinted primer saves a third finish coat), stains or tannin bleed (stain-blocking primer), and glossy or patched surfaces (bonding or spot primer so the finish coat adheres and dries uniform). Skipping primer on new drywall is the classic callback — the paper and the joint compound absorb paint at different rates and every seam telegraphs through.
Should I subtract windows and doors when calculating paint?
Use 20 SF per door and 15 SF per average window. On rooms with only one or two openings, many pros skip the deduction and treat it as a built-in waste and touch-up allowance. Always deduct large openings — garage doors, sliders, storefront glass — because at that scale the deduction changes the gallon count.
How do I estimate paint for ceilings and trim?
Measure them separately from walls. Ceilings are length times width — a 12 x 14 ceiling is 168 SF, about half a gallon per coat of flat ceiling paint. Trim is counted in linear feet of base, casing, and crown; as a rule of thumb a gallon of trim enamel handles roughly 350-400 SF of brushed surface, and most rooms need only a quart or two — but it is a different product than wall paint, so it must be its own line.