# Paint Calculator

Area and coats to gallons and buckets.

- Page: https://jianzhujisuan.com/en/paint-gallons
- Category: Finishes (https://jianzhujisuan.com/en/c/finishes)
- Chinese version: https://jianzhujisuan.com/zh/paint-gallons.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Painting area 800 ft², Number of coats 2 coats, Coverage per gallon 350 ft²/gal, Primer coat No (same colour)): **Paint required 4.6 gal**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Painting area | number | 800 | ft² |  |
| Number of coats | number | 2 | coats |  |
| Coverage per gallon | number | 350 | ft²/gal |  |
| Primer coat | select | No (same colour) | — |  |

## Formula

- **Coats = topcoats + primer if selected**: 
- **Gallons = area × coats ÷ coverage**: 
- **Whole gallons = round up**: no half-gallon mixing
- **Buckets = 5 gal pails + 1 gal cans**: 

## Worked example

800 ft² at 2 coats and 350 ft²/gal: 2 x 800 / 350 = 4.6 gallons, so buy 5. Add a primer coat and it becomes 3 x 800 / 350 = 6.9, so 7 gallons.

## Questions

### How many square feet does a gallon cover?

Interior flat latex is labelled 350-400 ft²/gal per coat. In practice 400 on smooth drywall, 300 on textured or previously painted walls and 250 on rough exterior boards. Dark to light and low-opacity pigments like reds and yellows cover less and may need three coats. Read the can, then order on the low side of it.

### Is primer really necessary?

On new drywall, patched walls, bare timber and metal it is mandatory, and it saves money rather than costing it. Those substrates are so absorbent that the first topcoat is half drunk in, forcing two more coats to even out - more paint in total than primer plus two topcoats, plus the patchy sheen known as flashing. Same-colour repaints over sound old paint can skip it.

### Is a 5 gallon pail worth it?

The unit price is typically 20-35% lower, but only if you genuinely need 5 gallons in one colour. A whole house in one off-white justifies a pail; several rooms in different colours does not. Also note a pail cannot be poured straight into a tray - decant it - and left open for two days it skins over, so seal it properly.

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