The paint coverage calculator determines the precise paint volume in gallons required to paint interior rooms. By combining room perimeter dimensions, ceiling height, coat counts, and automatic deductions for doors and windows, it avoids costly paint shortages or excessive leftover cans.

### Wall Area & Paint Formulas

The calculator applies standard professional painting metrics: - **Perimeter:** $\text{Perimeter} = 2 \times (\text{Length} + \text{Width})$ - **Gross Wall Area:** $\text{Gross Area} = \text{Perimeter} \times \text{Ceiling Height}$ - **Door Deductions:** Standard door allowance of $21\text{ sq ft}$ per door. - **Window Deductions:** Standard window allowance of $15\text{ sq ft}$ per window. - **Net Paintable Area:** $\text{Net Area} = \max(0, \text{Gross Area} - \text{Door Area} - \text{Window Area})$ - **Total Coverage Needed:** $\text{Total Area} = \text{Net Area} \times \text{Coats}$ - **Purchased Paint Volume:** $\text{Gallons} = \lceil \text{Total Area} / 350 \rceil$ (based on the standard coverage benchmark of 350 sq ft per gallon).

### Worked Sizing Example

For a standard master bedroom measuring $16\text{ ft}$ long by $12\text{ ft}$ wide with $9\text{ ft}$ ceilings, 2 doors, 2 windows, and 2 coats of paint: 1. Perimeter: $2 \times (16 + 12) = 56\text{ ft}$. 2. Gross wall area: $56 \times 9 = 504\text{ sq ft}$. 3. Deductions: $(2 \times 21) + (2 \times 15) = 42 + 30 = 72\text{ sq ft}$. 4. Net wall area per coat: $504 - 72 = 432\text{ sq ft}$. 5. Total area for 2 coats: $432 \times 2 = 864\text{ sq ft}$. 6. Gallons required: $864 / 350 = 2.47\text{ gallons} \rightarrow$ round up to **3 Gallons**.

### Client-Side Execution Note

Calculations update dynamically as you enter room dimensions or adjust coat counts. All arithmetic runs in your local browser session without server calls.