📐 Room Size Calculator
Enter a room's length, width, and ceiling height to find its floor area, wall area, and volume — plus the flooring boxes and paint gallons you'll need.
📏 Length, Width & Height
What is a Room Size Calculator?
It turns three simple measurements — length, width, and ceiling height — into the numbers a project actually needs. It computes floor area for flooring and furniture planning, wall area for paint and wallpaper, and volume for HVAC and air-quality sizing, then converts those into shopping quantities: how many boxes of flooring and gallons of paint to buy, with sensible waste and coverage allowances built in.
Use it to budget a refresh, avoid a second trip to the store, or check that new furniture will fit the space. The quantities are estimates for planning — confirm coverage on the product label and measure twice before you buy.
❓ Frequently Asked Questions
How does the calculator estimate flooring and paint?
Flooring is based on floor area: it assumes 20 square feet per box and adds a 10% waste allowance for cuts and mistakes, then rounds up to whole boxes. Paint is based on wall area (the room perimeter times the ceiling height): it assumes 350 square feet of coverage per gallon over two coats, again rounded up. Buy whole units, so the rounded figures are what you'll actually purchase.
Why does it ask for the ceiling height?
Ceiling height drives both the wall area and the room volume. Wall area is what you paint and is needed to size paint correctly, while volume (floor area times height) matters for HVAC sizing, dehumidifiers, and air purifiers. The default is a standard 8 feet, but tall or vaulted ceilings change these numbers significantly, so enter your actual height.
Does it account for doors and windows when painting?
No — it calculates the full wall area, which slightly overestimates paint for rooms with large windows or many doors. That extra is usually welcome, since you'll want some paint left over for touch-ups, and the two-coat assumption already builds in a margin. For a precise figure, subtract the area of major openings from the wall area before buying.