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Room Repaint Calculator Sequence

Repaint a room in the right order: measure wall area, check the volume for ventilation, repair the board, then work out gallons, rolls and total cost.

Repainting is the most commonly underestimated job in a house, and almost always for the same reason: paint is bought against floor area instead of wall area. A 12 by 10 ft room has 120 ft2 of floor and 352 ft2 of wall, and the paint has to cover the wall.

This sequence starts with the measurement that actually matters, checks whether the surface needs work before any paint goes on, and finishes with a priced list. The touch-up allowance near the end is worth doing: matching a colour six months later is far harder than buying an extra quart now.

Calculators in order

  1. Step 1: Square Footage CalculatorWall area from the room perimeter and ceiling height.
  2. Step 2: Room Volume CalculatorVolume matters for ventilation and drying time.
  3. Step 3: Drywall CalculatorPatch or replace board before any paint goes on.
  4. Step 4: Paint CalculatorGallons for the coats you actually plan to apply.
  5. Step 5: Wallpaper CalculatorOr rolls, if one wall is going to be papered instead.
  6. Step 6: Project Waste Factor CalculatorTouch-up allowance so you are not colour-matching later.
  7. Step 7: Material Cost CalculatorPaint, primer, sundries and board as one list.
  8. Step 8: Project Budget CalculatorTotal the room, with labor if you are hiring it out.

What you end up with

Gallons by coat, any board and compound needed for repairs, a touch-up allowance, and the whole thing priced.

Questions about this project

Should I measure floor area or wall area to buy paint?
Wall area, always. Multiply the room perimeter by the ceiling height, then deduct doors and windows. Floor area and wall area are not proportional: a long narrow room has far more wall per square foot of floor than a square room of the same size.
Do I need to repair drywall before painting?
Fix it first, because paint makes flaws more visible rather than less. Fresh compound and bare patches also absorb paint at a different rate than the surrounding wall, so an unprimed repair shows through the finish coat as a dull spot even when the colour matches.
How much extra paint should I buy?
Enough for touch-ups, which usually means rounding up to the next container rather than adding a percentage. Paint is sold in fixed sizes, so a calculated 1.7 gallons becomes 2 gallons anyway. Keep the leftover sealed and labelled with the room name.

Other project workflows

Last updated: 2026-08-03