# Wall Paint Calculator

Free wall paint calculator. Enter room dimensions or square feet for interior or exterior wall paint. Subtracts doors and windows, shows gallons, liters, and cost.

## What this calculates

Run out of paint halfway through the job and the new gallon never quite matches. Buy two extra gallons and they sit in the garage for a decade. This wall paint calculator gives you the exact number of gallons (and liters) for any room or exterior wall, factoring in the number of coats, coverage rate, and the square footage of doors and windows you are not painting.

## Inputs

- **Input Method** — options: Room dimensions (length x width x height), Direct wall square feet — Enter room dimensions or total wall area directly
- **Room Length** (ft) — min 0 — Longest wall. Ignored if using direct sq ft.
- **Room Width** (ft) — min 0
- **Ceiling Height** (ft) — min 0 — Standard US residential is 8 ft; newer homes often 9-10 ft
- **Total Wall Square Feet** (sq ft) — min 0 — Use the wall paint calculator square feet mode when you already measured wall area
- **Paint Location** — options: Interior (350 sq ft/gal), Exterior wall paint (300 sq ft/gal), Textured / rough surface (250 sq ft/gal) — Exterior wall paint calculator coverage drops on rough surfaces
- **Number of Coats** — min 1, max 5 — 2 is standard. Use 3 for dramatic color changes.
- **Doors to Subtract** — min 0, max 20 — Standard door = ~21 sq ft
- **Windows to Subtract** — min 0, max 30 — Standard window = ~15 sq ft
- **Price per Gallon** ($) — min 0 — Interior $25-70/gal, exterior $35-80/gal typical

## Outputs

- **Gross Wall Area** (sq ft)
- **Paintable Area** (sq ft) — Gross area minus doors and windows
- **Gallons Needed (exact)** (gal)
- **Gallons to Order** (gal) — Rounded up to whole gallons
- **Liters Needed** (L)
- **Estimated Cost** — formatted as currency

## Details

## How the Wall Paint Calculator Works

Paint needs come down to one formula: **gallons = (paintable area x number of coats) / coverage rate per gallon**. The calculator does two things before that:

1. **Computes wall area.** From room dimensions: perimeter x ceiling height. In direct-entry mode, the wall paint calculator square feet you enter is used as-is.
2. **Deducts openings.** Each standard door = 21 sq ft, each standard window = 15 sq ft. Small windows and large picture windows should be measured individually.

Then it divides by the coverage rate: **350 sq ft/gal** for standard interior latex on smooth drywall, **300 sq ft/gal** for exterior wall paint on primed siding, and **250 sq ft/gal** on textured or rough masonry.

## Exterior Wall Paint Calculator Coverage

An exterior wall paint calculator has to account for a rougher surface and higher UV / weather load. Coverage drops from 350 to about 300 sq ft/gal on primed lap siding, 250 on rough stucco or brick, and as low as 200 on split-face block. Exterior latex also needs a thicker mil build, meaning you often apply 2 full coats even when the color barely changes. Buy 10-15% extra for exterior jobs.

## Wall Paint Calculator Square Feet Reference

If you know the wall square feet already and just need gallons, use the direct square feet mode. Quick reference for common rooms at 8 ft ceilings:

| Room | Dimensions | Wall Sq Ft | Gallons (2 coats, no openings) |
|---|---|---|---|
| Small bedroom | 10 x 10 | 320 | 2 |
| Master bedroom | 14 x 16 | 480 | 3 |
| Living room | 16 x 20 | 576 | 4 |
| Kitchen | 10 x 14 | 384 | 3 |
| Hallway | 3 x 20 | 368 | 3 |

## Exterior Wall Paint Example

A 2,000 sq ft two-story home has roughly 2,500-3,000 sq ft of exterior wall area after deducting windows and doors. At 300 sq ft/gal coverage and 2 coats, that is 17-20 gallons of exterior paint. Add 1 gallon for touch-ups and trim, call it 20 gallons at $50/gal = $1,000 in paint alone, before primer, caulk, and labor.

## Coverage Rate Tips

- **Primer counts separately.** If you are painting over dark walls, stains, or new drywall, add a primer gallon on top of the topcoat count. Primer covers about 200-300 sq ft/gal.
- **Low-sheen and matte finishes cover slightly less** than semi-gloss and gloss on the first coat because they are thicker.
- **Dark-to-light color changes** often need 3 coats, not 2. Use a tinted primer to cut this to 2 coats.
- **Ceiling paint is separate** from this wall paint calculator. One gallon covers about 350-400 sq ft of ceiling.

## Frequently Asked Questions

**Q: How do I use the wall paint calculator square feet mode?**

A: Switch the input method to 'Direct wall square feet' and enter the total wall area you measured. This is useful when walls are irregular (vaulted ceilings, bump-outs, half walls) or when you already calculated square footage on a floor plan. The calculator then multiplies by coats and divides by the coverage rate of 350 sq ft/gal (interior) or 300 sq ft/gal (exterior wall paint).

**Q: How does an exterior wall paint calculator differ from interior?**

A: Exterior wall paint calculator coverage is lower (about 300 sq ft/gal vs 350 interior) because siding, stucco, and masonry are rougher and the paint mil build is thicker. Exterior paint is also formulated to flex with temperature changes, resist UV, and lock in against wind-driven rain. Always use exterior-rated paint outside, interior-rated inside, never mix them.

**Q: How much paint for a 12x12 bedroom?**

A: A 12 x 12 room with 8 ft ceilings has 384 sq ft of wall area (perimeter 48 ft x 8 ft). Subtract one door (21 sq ft) and two windows (30 sq ft) = 333 sq ft paintable. At 350 sq ft/gal coverage and 2 coats, that is 1.9 gallons. Buy 2 gallons, which leaves enough for touch-ups and a future closet.

**Q: Does this wall paint calculator include primer?**

A: No. The calculator assumes you are applying a top coat over a surface already sealed or previously painted. If you are painting over bare drywall, heavy stains, dark colors, or new masonry, calculate primer separately. Primer typically covers 200-300 sq ft/gal, slightly less than paint. Plan on 1 primer coat and 2 top coats for most projects.

**Q: How do I measure wall square feet accurately?**

A: Measure the length of each wall along the floor, add them together (the perimeter), and multiply by the ceiling height. Example: a 10 x 14 room has perimeter (10 + 14 + 10 + 14) = 48 ft, x 8 ft ceilings = 384 sq ft. For vaulted ceilings, break the wall into a rectangle plus a triangle (base x height / 2). Subtract standard doors (21 sq ft) and windows (15 sq ft) separately.

**Q: How many coats of wall paint do I need?**

A: Two coats is standard for most projects. Go to 3 coats if: you are going from dark to light, repainting over a stain or water mark, using economy paint, or covering a bright accent wall with a neutral color. A tinted primer can cut 3 coats back to 2 and is usually cheaper than an extra gallon of topcoat.

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Source: https://vastcalc.com/calculators/construction/wall-paint
Category: Construction
Last updated: 2026-04-08