# Paint Amount Calculator

Paint amount calculator that returns exact gallons, liters, and rounded order quantity. Handles interior, exterior, and textured surfaces with door, window, and waste deductions.

## What this calculates

Buy too little paint and the next gallon never matches. Buy too much and you pay for cans that sit in the garage for a decade. This paint amount calculator gives you an exact gallon figure (and a practical order quantity) for any interior, exterior, or textured project, with standard door and window deductions plus a waste allowance for touch-ups.

## Inputs

- **Paintable Wall Area** (sq ft) — min 0 — Total wall area to be painted, before door and window deductions.
- **Surface Type** — options: Interior smooth drywall (350 sq ft/gal), Exterior primed siding (300 sq ft/gal), Textured / rough surface (250 sq ft/gal), Rough masonry or stucco (200 sq ft/gal), Custom coverage rate (enter below) — Paint amount calculator coverage varies by surface.
- **Custom Coverage Rate** (sq ft/gal) — min 50, max 600 — Only used when Surface Type = Custom.
- **Number of Coats** — min 1, max 5 — Two coats is standard. Use 3 for dark-to-light color changes.
- **Standard Doors to Subtract** — min 0, max 20 — Each door = 21 sq ft (standard 3' x 6'8").
- **Standard Windows to Subtract** — min 0, max 30 — Each window = 15 sq ft (standard 3' x 5').
- **Waste Allowance** (%) — min 0, max 30 — Extra paint for touch-ups and spills. 10% is typical.
- **Price per Gallon** ($) — min 0 — Interior $25-70, exterior $35-80 per gallon.

## Outputs

- **Paintable Area** (sq ft) — Wall area minus doors and windows
- **Total Coverage Needed** (sq ft) — Paintable area times number of coats
- **Paint Amount (exact)** (gal)
- **Paint Amount with Waste** (gal) — Exact need plus waste allowance
- **Gallons to Order** (gal) — Rounded up to whole gallons
- **Liters Needed** (L)
- **Estimated Cost** — formatted as currency

## Details

## How the Paint Amount Calculator Works

The paint amount formula is simple:

**Gallons = (Paintable Area x Coats) / Coverage Rate**

Where:

- **Paintable area** = gross wall area minus standard doors (21 sq ft each) and windows (15 sq ft each)
- **Coats** = number of coats you plan to apply, typically 2
- **Coverage rate** = square feet a gallon covers on your surface

The calculator adds a waste allowance on top (default 10%) so you have enough for touch-ups, then rounds the total up to the next whole gallon because paint is sold in 1-gallon cans.

## Coverage Rates by Surface

These are the coverage rates published on Sherwin-Williams, Benjamin Moore, and Behr data sheets:

| Surface | Coverage per Gallon |
|---|---|
| Interior smooth drywall | 350 sq ft |
| Interior with mild texture | 300 sq ft |
| Exterior primed siding | 300 sq ft |
| Rough stucco or masonry | 200 sq ft |
| Split-face block or brick | 150 sq ft |
| Ceilings (flat) | 350-400 sq ft |

Textured or porous surfaces absorb more paint. If you are painting masonry for the first time, plan on 200 sq ft/gal for the first coat and 250-300 for the second.

## Example: 12x14 Bedroom

- Room: 12 x 14 ft, 8 ft ceilings
- Perimeter: (12+14+12+14) = 52 ft
- Gross wall area: 52 x 8 = 416 sq ft
- Openings: 1 door (21 sq ft) + 2 windows (30 sq ft) = 51 sq ft
- Paintable area: 416 - 51 = 365 sq ft
- 2 coats at 350 sq ft/gal: (365 x 2) / 350 = 2.09 gallons
- With 10% waste: 2.29 gallons
- Order: **3 gallons**

Three gallons leaves enough paint for touch-ups over the next few years, which is exactly when a scuff or wall repair will need it.

## Paint Amount for Common Rooms

| Room Size | Wall Area | Gallons (2 coats, no openings) |
|---|---|---|
| 10 x 10 bedroom | 320 sq ft | 2 |
| 12 x 14 bedroom | 416 sq ft | 3 |
| 14 x 16 master | 480 sq ft | 3 |
| 16 x 20 living room | 576 sq ft | 4 |
| 10 x 14 kitchen | 384 sq ft | 3 |

## Exterior Paint Amount

A 2,000 sq ft two-story home has roughly 2,500-3,000 sq ft of exterior wall after subtracting windows and doors. At 300 sq ft/gal and 2 coats:

- (2,750 x 2) / 300 = 18.3 gallons
- With 10% waste: 20.2 gallons
- Order: **21 gallons**

That's a typical full-house exterior repaint. At $50/gal that is $1,050 in paint alone, plus primer, caulk, and labor.

## When to Add More Coats

- **Dark to light color change:** plan on 3 coats, or use a tinted primer to cut to 2.
- **New drywall:** primer coat plus 2 top coats.
- **Staining or water damage:** stain-blocking primer plus 2 top coats.
- **Economy paint (under $20/gal):** often needs 3 coats where premium paint needs 2.

## Primer Is Separate

The paint amount calculator above handles the top coats. Primer has a different coverage rate (200-300 sq ft/gal) and is calculated as a single extra coat. For most repaints, primer is skipped; for new drywall, bare wood, or after patch repairs, calculate primer separately at 250 sq ft/gal.

## Tips for Accurate Paint Amount Estimates

- Measure wall by wall, then add. For vaulted or angled walls, break the shape into a rectangle plus a triangle (base x height / 2).
- Do not forget closets. A 5x7 walk-in with 8 ft ceilings adds 192 sq ft.
- Subtract only the openings you are not painting. Trim and the inside face of doors are usually painted and should not be deducted.
- If you plan to paint the ceiling, calculate ceiling paint separately. Use ceiling area (length x width) at 350 sq ft/gal.
- Always buy in the largest can you need. A 1-gallon can costs more per square foot than the same paint in a 5-gallon bucket.

## Frequently Asked Questions

**Q: How do I calculate the paint amount for a room?**

A: Measure the room perimeter (sum of wall lengths) and multiply by ceiling height to get gross wall area. Subtract 21 sq ft per standard door and 15 sq ft per standard window. Multiply by the number of coats, then divide by 350 sq ft/gal (interior smooth) to get gallons. For a 12 x 14 room with 8 ft ceilings, 1 door, and 2 windows: 416 - 51 = 365 sq ft paintable, x 2 coats = 730, / 350 = 2.09 gallons. Round up to 3 gallons to include touch-up.

**Q: How much paint amount do I need for a 12x12 room?**

A: A 12 x 12 room with 8 ft ceilings has 384 sq ft of gross wall area. Subtract 1 door (21 sq ft) and 2 windows (30 sq ft) = 333 sq ft paintable. At 350 sq ft/gal and 2 coats that is 1.9 gallons. Order 2 gallons minimum, 3 gallons if you want touch-up paint for the future. Same math works in this paint amount calculator for any square or rectangular room.

**Q: What is the paint amount formula?**

A: Paint Amount Formula: Gallons = (Paintable Area x Coats) / Coverage Rate. Paintable area is gross wall area minus door (21 sq ft each) and window (15 sq ft each) deductions. Coverage rate is 350 sq ft/gal for interior smooth drywall, 300 for exterior siding, 250 for textured, and 200 for rough masonry. Add 10-15% for waste and round up to whole gallons.

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

A: No. Primer has its own coverage rate (200-300 sq ft/gal) and is calculated as a separate layer. If you are painting bare drywall, new wood, or a dramatic color change, calculate primer separately using the same formula. For most repaints over existing paint in the same color family, primer is optional and is not included in the paint amount calculation.

**Q: How much paint amount is in a 5-gallon bucket?**

A: Exactly 5 US gallons, or about 18.9 liters. A 5-gallon bucket covers 1,750 sq ft at 350 sq ft/gal. That is enough for a typical 2,500 sq ft single-story home interior at 2 coats, or about 80% of a 2,000 sq ft exterior repaint. Five-gallon buckets cost 20-30% less per gallon than 1-gallon cans, so buy the bucket for any project needing 3+ gallons.

**Q: Should I buy extra paint for touch-ups?**

A: Yes. Plan for 10-15% waste over the calculated paint amount. A gallon or quart left over is invaluable for touch-ups when you scratch the wall moving furniture or patch a nail hole two years later. Store the leftover can upside-down with the lid hammered tight; inverted storage keeps a skin off the paint. Good paint stays usable for 5-7 years if stored correctly.

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