Everyday Life
Paint Coverage Calculator
Determine how many gallons or liters of paint are needed to cover walls and rooms.
Inputs
Results
0.0 Gallons
Paint Needed (Standard Gallons)
Gross Wall Area
450 sq ft
Deducted Area (Doors/Windows)
55 sq ft
Net Surface Area
395 sq ft
Total Painting Area (Multi-Coat)
790 sq ft
How It Works
The calculator computes wall surface area ($A_{gross} = L \times H$) and subtracts standard area constants for windows ($15\text{ sq ft}$) and doors ($21\text{ sq ft}$). It multiplies the net area by the coat count to determine total painting surface area: $A_{net} = (A_{gross} - \text{Deductions}) \times \text{Coats}$. Finally, it divides this by the coverage rating per gallon (standard default: $350\text{ sq ft/gallon}$).
Formula Used
Net Wall Area = (Length × Height × Number of Walls) − Doors − Windows
The gross area of the walls is computed. We subtract standard deductions for doors and windows to calculate the actual net surface area that requires painting.
Required Paint (Gallons) = (Net Wall Area × Number of Coats) / Coverage Per Gallon
This calculates the total volume of paint needed. The net area is multiplied by the number of coats, then divided by the coverage rate of a standard paint gallon.
Worked Example
Here is a step-by-step example of how these values are calculated:
Width
50 ft
Height
9 ft
Windows
2
Doors
1
Coats
2
Coverage
350 sq ft/gal
Result: Net Area: `399 sq ft`. Total Painting Area (2 coats): `798 sq ft`. Paint Required: `2.3 Gallons`.
Frequently Asked Questions
How much paint does a standard room require?
A standard 12x12 foot room with an 8-foot ceiling has about 384 square feet of wall space. Excluding doors and windows, this typically requires 1 gallon of paint per coat.
Should I round up the amount of paint I purchase?
Yes. It is highly recommended to round up to the nearest whole gallon to account for absorption by drywall, roller cling, spillages, and future touch-up needs.