Interior Painting Cost Calculator
Price an interior or exterior painting job from your own rates: paint and primer by the gallon, preparation hours, trim, access and sundries, with the cost per square foot at the end.
Why the Paint Is the Small Half
Enter the areas, the coats, the spread rate off the tin and your own rates, and this works out the gallons to buy, the preparation, the application, the trim and the access, then divides the total by the area painted. The line that decides most painting quotes is the preparation, and it is asked for in hours on purpose: a percentage applied to the paint cost is a guess dressed up as a method. Two honest quotes for the same rooms can differ by a factor of two, and the difference is almost never the paint.
Results
QUANTITIES
Paint is sold in whole cans, so the figure in brackets is what you buy rather than what goes on the wall.
How to Price a Painting Job
Paint is the small half. On a typical repaint the material is a minority of the invoice and the preparation decides the rest, which is why two honest quotes for the same rooms can differ by a factor of two. Get the gallons out of the area, the coats and the spread rate on the tin. Then price the preparation by the hour against what you actually found on the walk-round, because that is the number that makes or loses the job.
1. Measure the walls, then the ceiling separately
Perimeter times height for the walls, length times width for the ceiling. Keep them apart: ceilings take a different product, more masking and more time under the roller.
2. Subtract the big openings only
Take out doors and large windows. Leaving the small ones in covers the cutting-in around them, which takes longer than rolling the area they occupy.
3. Decide the coats before anything else
The same colour over a sound surface can be one coat. Light over dark, or any strong colour, is a primer plus two. That decision changes the gallons and the hours by more than any other single answer.
4. Take the spread rate off the tin
It is measured on a sealed, smooth surface. New drywall, bare plaster, render and old chalky exterior paint drink the first coat, and heavy texture increases the real surface area well beyond what you measured.
5. Count the preparation in hours
Filling, sanding, caulking, washing, scraping, spot-priming. Walk the rooms and count the repairs rather than applying a percentage. This is the line that separates a quote that pays from one that does not.
6. Price trim by the linear foot
Trim, doors and frames are slow work and they do not belong in a wall rate. A room with panelled doors, deep skirting and a picture rail can take longer than its walls.
7. Add access, sundries and the cans you have to buy whole
Scaffolding or a lift is a hire cost plus a setup day plus a strike day. Sundries are tape, sheets, rollers and disposal. And paint is sold in whole cans, so a job needing 4.2 gallons buys five.
Worked Example: a 12 x 14 Bedroom, Two Coats
9 foot ceilings, one door, one window, walls and ceiling both painted, spread rate taken from the tin at 350 square feet per gallon.
| Item | Working | Result |
|---|---|---|
| Wall perimeter | (12 + 14) x 2 | 52 ft |
| Gross wall area | 52 x 9 | 468 sq ft |
| Openings removed | door 21 + window 15 | −36 sq ft |
| Net wall area | 468 − 36 | 432 sq ft |
| Ceiling | 12 x 14 | 168 sq ft |
| Total area | 432 + 168 | 600 sq ft |
| Paint needed | 600 x 2 coats ÷ 350 | 3.43 gal |
| Paint to buy | whole cans | 4 gal |
Worked Example: an Exterior Repaint
1,800 square feet of siding in sound but faded condition, one coat over a wash and a scrape, two storeys, trim priced separately.
| Item | Working | Result |
|---|---|---|
| Siding area | measured | 1,800 sq ft |
| Paint needed | 1,800 x 1 coat ÷ 350 | 5.14 gal |
| Paint to buy | whole cans | 6 gal |
| Spot priming | bare wood found on the walk-round | its own hours |
| Preparation | wash, scrape, sand, caulk | the majority of the labour |
| Access | two storeys | scaffolding, plus a day up and a day down |
| Weather | a window that can close | schedule risk, not a line item |
What Decides the Number of Coats
Coats multiply both the paint and the hours, so this is the first question to settle.
| Situation | Coats | Note |
|---|---|---|
| Same colour, sound surface | 1 | A refresh rather than a repaint |
| Light over light, different colour | 2 | The normal case |
| Light over dark, or a strong colour | primer + 2 | The primer is what stops the third coat |
| New drywall or bare plaster | primer + 2 | The first coat is absorbed, not applied |
| Stains, smoke or water marks | stain-blocking primer + 2 | Ordinary primer will not hold it back |
Where the Hours Actually Go
None of these are paint, and together they are most of the invoice.
Masking and putting back
In an occupied house, covering furniture and floors and then restoring the room every evening is real time that produces nothing visible. An empty house is a different quote.
Repairs before paint
Filling, skimming a badly patched wall, sanding out old brush ridges, caulking gaps at the trim. Count them on the walk-round, because a wall that looks fine from the doorway rarely is.
Cutting in
Edges, corners, ceiling lines and around every fitting. It is slow, it is skilled, and it does not shrink when the room does.
Access
Stairwells, double-height spaces and two-storey exteriors are priced on how you reach them before they are priced on area.
Weather, on the outside
A day lost to rain is a day paid for. Build the risk into the schedule rather than into a lower price.
Where Estimates Go Wrong
Pricing from the square footage alone
Two rooms of the same size in different condition are different jobs. The area sets the paint; the condition sets the hours, and the hours are the bigger number.
Trusting the spread rate on new drywall
The figure on the tin assumes a sealed surface. Unprimed board absorbs the first coat, and a job priced without a primer coat runs out of paint and out of hours at the same time.
Folding trim into the wall rate
Trim is linear-foot work at a slower pace. A house with a lot of it will lose money at a wall rate every time.
Forgetting that paint comes in whole cans
A job needing 4.2 gallons buys five. On a small job that rounding is a noticeable share of the material cost.
Quoting an exterior without a proper look at the substrate
Failed paint, rot and bare wood are found on a ladder, not from the driveway. The scraping and priming they need is the difference between a job that lasts twelve years and one that peels in three.
Painting Cost — Common Questions
What does interior painting cost?
The paint is the small half of it. The number is set by how many coats the colour change forces, how much filling, sanding and caulking the walls need first, how much trim there is, and whether the house is occupied and has to be masked and restored every day. Price the gallons from the area and the preparation from the walk-round.
How much paint do I need for a room?
Area times coats, divided by the spread rate on the tin, rounded up to whole cans. A 12 by 14 room with 9 foot ceilings and a painted ceiling is about 600 square feet, which at two coats and 350 square feet per gallon is 3.4 gallons, so four cans.
Why is exterior painting more expensive than interior?
Preparation and access. Washing, scraping, sanding back failed paint, spot-priming bare wood and replacing rotten trim is usually the majority of the labour, and anything above ladder height brings scaffolding with a setup day and a strike day. The weather can also stop the job for a week.
Should I charge by the square foot or by the hour?
Quote a fixed price, but build it from hours. A per-square-foot rate hides the preparation, which is the part that varies most between two jobs of the same size, and it is where a painting quote goes wrong.
Does the customer supplying the paint make it cheaper?
It makes your invoice smaller, not the job cheaper, and it moves the risk. If they under-buy or buy the wrong sheen the job stops. Put the quantity and the product in writing before they order.
How do I price a colour change from dark to light?
As a primer plus two coats, not as three coats of the finish. A tinted primer covers in one pass what two coats of finish paint will struggle with, and it is usually cheaper per gallon as well.
What is a fair preparation allowance?
There is not one, which is the point. Walk the rooms, count the repairs and put hours against them. Any percentage applied to the paint cost is a guess dressed up as a method.
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