# Paint Requirement Calculator

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

## What this calculates

Get the paint requirement right and you avoid two costly mistakes: running short halfway through a wall (and fighting to color-match the next gallon), or hauling home three extra cans that sit in the garage until the paint separates. This paint requirement calculator gives you an exact gallon figure plus a practical order quantity for interior, exterior, textured, or masonry projects, with standard door and window deductions and a waste allowance for touch-ups.

## Inputs

- **Wall Area to Paint** (sq ft) — min 0 — Gross wall area before door and window deductions
- **Surface Type** — options: Interior smooth drywall (350 sq ft/gal), Interior mild texture (300 sq ft/gal), Exterior primed siding (300 sq ft/gal), Heavy texture or popcorn (250 sq ft/gal), Rough masonry / stucco (200 sq ft/gal), Custom coverage (enter below)
- **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 (3 ft x 6 ft 8 in)
- **Standard Windows to Subtract** — min 0, max 30 — Each window = 15 sq ft (3 ft x 5 ft)
- **Waste Allowance** (%) — min 0, max 30 — Extra paint requirement 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 Requirement (exact)** (gal)
- **Paint Requirement with Waste** (gal)
- **Gallons to Order** (gal) — Rounded up to whole gallons
- **Liters Needed** (L)
- **Estimated Cost** — formatted as currency

## Details

## How the Paint Requirement Calculator Works

The paint requirement formula is:

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

Where:

- **Paintable area** = gross wall area minus standard doors (21 sq ft each) and windows (15 sq ft each)
- **Number of coats** = 2 for most repaints, 3 for dark-to-light color changes
- **Coverage rate** = square feet a gallon covers on your chosen surface

The calculator adds a waste allowance on top (default 10%) for touch-ups and spills, then rounds up to whole gallons because paint is sold in 1-gallon cans or 5-gallon buckets.

## Coverage Rates by Surface Type

These are the coverage rates published on 2025 Sherwin-Williams, Benjamin Moore, and Behr data sheets:

| Surface Type | Coverage per Gallon |
|--------------|---------------------|
| Interior smooth drywall | 350 sq ft |
| Interior mild texture | 300 sq ft |
| Exterior primed siding | 300 sq ft |
| Heavy texture or popcorn ceiling | 250 sq ft |
| Rough masonry or stucco | 200 sq ft |
| Split-face block or brick | 150 sq ft |

Textured or porous surfaces absorb more paint. First coat on bare masonry often needs 150 sq ft/gal; second coat recovers to 250 sq ft/gal as the surface seals.

## Worked Example: 12 ft x 14 ft Bedroom

- Room: 12 x 14 ft with 8 ft ceilings
- Perimeter: 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**
- At 350 sq ft/gal and 2 coats: (365 x 2) / 350 = **2.09 gallons**
- With 10% waste: 2.29 gallons
- Paint requirement to order: **3 gallons**

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

## Paint Requirement for Common Room Sizes

At 8 ft ceilings, 2 coats, interior smooth drywall, 1 door and 2 windows subtracted:

| Room | Gross Wall Area | Paintable Area | Gallons |
|------|-----------------|----------------|---------|
| 10 x 10 bedroom | 320 sq ft | 269 | 2 |
| 12 x 12 bedroom | 384 sq ft | 333 | 2 |
| 12 x 14 bedroom | 416 sq ft | 365 | 3 |
| 14 x 16 master | 480 sq ft | 429 | 3 |
| 16 x 20 living room | 576 sq ft | 525 | 4 |
| 10 x 14 kitchen | 384 sq ft | 333 | 2 |

## Paint Requirement for an Entire House

Typical interior repaints of a single-story 2,000 sq ft home with 8 ft ceilings, all rooms:

- Gross wall area: approximately 4,500 to 5,500 sq ft
- After door/window deductions: 3,800 to 4,800 sq ft paintable
- At 2 coats and 350 sq ft/gal: 22 to 28 gallons

Order a 5-gallon bucket plus a few 1-gallon cans rather than 25 individual gallons. Five-gallon buckets run 20 to 30% less per gallon.

## Exterior Paint Requirement

A 2,000 sq ft two-story home has roughly 2,500 to 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
- Paint requirement to order: **21 gallons**

At $50/gal that is $1,050 in paint alone, plus primer, caulk, and labor for a pro repaint.

## When to Add More Coats

- **Dark to light color change:** 3 coats, or tinted primer plus 2 top coats
- **New drywall:** primer plus 2 top coats
- **Stain or water damage:** stain-blocking primer plus 2 top coats
- **Economy paint (under $20/gal):** typically 3 coats for coverage

## Primer Is a Separate Calculation

The paint requirement above covers top coats only. Primer has its own coverage rate (200 to 300 sq ft/gal). For most repaints over existing paint in the same color family, primer is optional. For new drywall, bare wood, stain spots, or dramatic color changes, calculate primer separately at 250 sq ft/gal.

## Tips for an Accurate Paint Requirement

- Measure wall by wall, then sum. For vaulted or angled walls, break into a rectangle plus a triangle (base x height / 2).
- Do not forget closets. A 5 x 7 walk-in with 8 ft ceilings adds 192 sq ft of wall.
- Subtract only openings you will not paint. Trim and the inside face of doors are usually painted and should not be deducted.
- Ceilings are a separate calculation: use ceiling area (length x width) at 350 sq ft/gal.
- Buy in 5-gallon buckets for any project needing 3+ gallons.

## Frequently Asked Questions

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

A: Measure the room perimeter and multiply by ceiling height to get gross wall area. Subtract 21 sq ft per door and 15 sq ft per window. Multiply by the number of coats (usually 2), divide by 350 sq ft/gal for interior smooth drywall, then add 10% waste. 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 including touch-up.

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

A: Paint requirement formula: Gallons = (Paintable Area x Number of 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, 200 for rough masonry. Add 10 to 15% for waste and round up to whole gallons.

**Q: How many gallons of paint for a 1,000 sq ft wall area?**

A: For 1,000 sq ft of paintable interior smooth drywall at 2 coats: (1,000 x 2) / 350 = 5.71 gallons exact, 6.28 gallons with 10% waste, round up to 7 gallons. For exterior siding at 300 sq ft/gal, the paint requirement is 6.67 gallons exact, 7.33 with waste, round up to 8 gallons.

**Q: How much paint requirement for a 2,000 sq ft house exterior?**

A: A 2,000 sq ft house has roughly 2,500 to 3,000 sq ft of exterior wall area after door and window deductions. At 300 sq ft/gal and 2 coats: 18 to 20 gallons exact, 20 to 22 gallons with 10% waste. Order 21 gallons (one 5-gallon bucket plus 16 single gallons, or five 5-gallon buckets for a trim-and-body color combo).

**Q: Does the paint requirement include primer?**

A: No. Primer has its own coverage rate (200 to 300 sq ft/gal) and is calculated as a separate layer. For bare drywall, new wood, or dramatic color changes, calculate primer separately using the same paintable area divided by 250 sq ft/gal. For most repaints over existing paint in the same color family, primer is optional and is not included in the main paint requirement.

**Q: Should I add waste to the paint requirement calculation?**

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

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