Gallons needed
2.10
Paintable area
420 sq ft
Gallons to buy
3

Openings deducted at 10 sq ft per window and 20 per door. A quart covers about 100 sq ft, so a 2.1 gallon result is 2 gallons plus a quart rather than 3.

Full calculator — primer, surfaces, colour change and the cheapest tin mix