120 sq ft
Interior Remodel Calculator
Enter a room's length, width, ceiling height, and door/window openings once and get floor/wall area, drywall sheets, insulation coverage, and paint gallons together.
Material ListFloor area Drywall sheets to buy Cavity volume Primer Topcoat
An interior remodel almost always touches drywall, insulation, and paint over the same room footprint. This page runs Room Layout once to get floor area, wall area, and perimeter, then feeds that straight into the Drywall, Insulation, and Paint calculators. Each calculator below is the same one available on its own page — nothing here is a new formula, it is Room Layout’s output read the same way Drywall/Insulation/Paint already read a shared room layout on their standalone pages.
Drywall sheet counts from room dimensions
Drywall sheet count is wall area plus ceiling area, divided by the coverage of one sheet, with a waste allowance rounded up to a whole sheet — the same math as buying fixed-size sheets from the yard. Wall area here comes directly from Room Layout’s perimeter times ceiling height, minus door and window openings, so changing the room’s length, width, or ceiling height updates the drywall count automatically.
Standard sheets are 4x8 ft, but 4x12 sheets are common on taller walls to cut down on horizontal seams. Waste accounts for cuts around outlets, corners, and openings.
Room dimensions and openings
Enter room length, width, ceiling height, and openings once. Drywall, insulation, and paint each add a few fields of their own below (sheet size, target R-value, coverage rates) that a room's dimensions alone don't determine.
Room Layout
Floor area, wall area, and perimeter from room length, width, and ceiling height — the shared backbone for Drywall, Insulation, and Paint below.
This room has 319.99 sq ft of wall and 120 sq ft of floor.
This room has
Room Layout result
Detail values
- Floor area
- 120 sq ft
- Perimeter
- 44 ft
- Wall area
- 319.99 sq ft
- Wall segments
- 12.00, 10.00, 12.00, 10.00 ft
Assumptions
Formula details
- Floor area: 0.5 x abs(sum(xi x yi+1 - xi+1 x yi))
Drywall
Drywall sheets to buy from the room's wall and ceiling area, sheet size, and waste percent.
You'll need 16 sheets of drywall for 439.99 sq ft.
You'll need
Drywall result
16 sheets
Warnings
- INFO Material estimate only. Verify layout, cuts, and field conditions before purchase.
Detail values
- Total area
- 439.99 sq ft
- Sheet area
- 32 sq ft
- Base sheets
- 13.75
Assumptions
- Sheet size: 4 × 8 ft (editable)
- Waste: 10% (editable)
Formula details
- Purchase sheets: ceil((wallArea + ceilingArea) / sheetArea × (1 + waste%))
Insulation
Coverage units or cavity volume and delta R-value for the room's walls.
You'll need 93.33 cu ft of insulation for 319.99 sq ft.
You'll need
Insulation result
93.33041666666668 cu ft
Warnings
- WARNING Required insulation depth exceeds the entered cavity depth.
- INFO Reference estimate only. Use product-label coverage and locally applicable requirements.
Detail values
- Delta R
- 13
- Estimated R
- 12.95
- Required depth
- 3.51 in
Assumptions
- R per inch: 3.7 (editable)
- Coverage: 50 sq ft/unit (editable)
Formula details
- Delta R: targetR - currentR
- Estimated R: cavityDepth × RPerInch
Paint
Primer and topcoat gallons for the room's wall area.
You'll need 4 gal of paint to cover 319.99 sq ft.
You'll need
Paint result
2 gal
2 gal
Detail values
- Total gallons
- 4
Assumptions
- Primer coverage: 300 sq ft/gal (editable)
- Topcoat coverage: 350 sq ft/gal (editable)
- First coat on raw drywall: No
Formula details
- Topcoat: ceil(area × coats / coverage)
Insulation R-value basics
Insulation on this page can be estimated two ways: by cavity depth and an R-per-inch rating for the product, or by entering a known R-value directly. Delta R (target minus current) shows how much more insulating value the wall needs to reach code or design targets — a wall already at or above target doesn’t need more.
Coverage area for insulation is the room’s wall area from Room Layout, the same area feeding Drywall, since insulation typically goes into the same wall cavities being closed up with drywall.
Paint coverage math
Paint gallons divide wall area by a coverage rate (typically 300-400 sq ft per gallon, but check the product label) and multiply by the number of coats, rounding up to a whole gallon. Primer is optional and uses its own coverage rate — skip it on previously painted walls in good condition, or keep it on for bare drywall, patched areas, or a major color change.
This page paints wall area only, not the ceiling — a common scope for a room repaint versus a full gut remodel. If ceiling paint is part of the job, add its area to the topcoat gallons separately.
FAQ
Why is Room Layout shown as its own result instead of just feeding the other three?
Floor area, wall area, and perimeter are useful numbers on their own when scoping a remodel, so this page shows the Room Layout result directly, the same as the standalone Room Layout calculator, in addition to feeding Drywall, Insulation, and Paint below it.
Does Paint cover the ceiling too?
No, this page paints wall area only. If the job includes ceiling paint, add the ceiling area to the topcoat gallons separately or use the standalone Paint calculator with a combined area.
Can I fine-tune just one calculator without changing the room dimensions?
Yes. Flip any section to "Manual entry" to edit its inputs directly without changing the room layout or the other calculators.
How do I enter multiple doors and windows?
List each opening as width x height in feet, separated by commas — for example "3x6.67, 3x4" for a standard door and a window.
Disclaimer
Material estimate and general reference only. Verify local code, manufacturer coverage rates, and field conditions before ordering or starting work.