Calculate net ceiling surface area for flat, multi-section, sloped, vaulted, or known-area ceilings, with optional opening deductions, extra allowance, conversions, and cost.
Dimensions are normalized before shared rectangle, triangle, hypotenuse, and roof-slope helpers calculate surface area. Room height is not required.
The calculator follows gross area → deductions → net area → optional extra allowance. It measures ceiling surfaces without estimating a specific material.
area = length × width × quantitysurface area = ceiling length × horizontal run × √(1 + (rise ÷ run)²)area = 2 × room length × √((room width ÷ 2)² + ridge rise²)net area = gross ceiling area − entered deductionsplanning area = net area × (1 + extra percentage ÷ 100)A 12 × 15 ft flat ceiling has 180 ft² of area.
A 20 ft ceiling length with a 10 ft horizontal run and 6:12 pitch has a 1.118034 slope factor, about 11.18034 ft sloped width, and about 223.6068 ft² surface area.
A centered 20 × 16 ft vault with a 4 ft ridge rise has an 8 ft half-span, about 8.94427 ft sloped length per side, and about 357.7709 ft² surface area.
A 300 ft² ceiling minus a 4 × 6 ft opening has 276 ft² net area. A 10% allowance produces 303.6 ft².
Divide L-shaped or irregular ceilings into rectangles and triangles, then add each section.
Large skylights and stair or attic openings may be useful deductions; small fixtures and vents are not subtracted automatically.
Paint, drywall, insulation, panels, and tile require their own coverage and purchase assumptions.
For a rectangular room, flat ceiling area equals floor area. Multiple-section mode supports rectangles, triangles, and known-area sections with independent units and quantities.
The horizontal plan area is multiplied by the shared roofing slope factor. Rise and run form a dimensionless ratio, so metric and US users can enter the same pitch ratio.
The v1 vault assumes a centered ridge, two equal rectangular planes, and no flat center. Ridge rise is measured vertically from the wall top to the ridge.
Sloped and vaulted results compare horizontal projected area with actual surface area, including the added area and percentage increase.
Raw calculations retain square meters internally and use the shared conversion system for square feet, square meters, and square yards.
Multiply ceiling length by width for a flat rectangle.
It is the same for a simple flat rectangular room, but not for sloped or vaulted ceilings.
Multiply horizontal projected area by the slope factor derived from rise and run.
For a centered two-plane vault, find the sloped length from half the room width and ridge rise, multiply by room length, then double it.
Each inclined plane is longer than its horizontal projection.
Add deductions only when those areas should be excluded from the intended planning surface.
Split the ceiling into rectangles, triangles, or known areas and add a section for each.
No. A flat ceiling uses length and width; a vault uses ridge rise relative to the wall top.
No. Use the related Paint or Drywall Calculator for material quantities.