What the paint calculators cover
Paint is counted by area, coats and spread rate, and every other page on this hub is a correction to one of those three. The room pages count surfaces: walls with their openings, ceilings, doors, frames and skirting, with the primer, the thinned mist coat for new plaster, the filler that an open block wall absorbs, the extra coats that light paint needs over a dark colour, and the masking and floor protection that go with the work.
The outdoor pages count a fence, a deck, a paver surface, a driveway sealcoat and railings measured by girth. The floor pages count epoxy and its primer, and the lines painted on a drive, a car park or a court. The steel pages count primer and intumescent coating from the surface area of the members. The last groups mix, tint and thin, and check the conditions and the losses that change what has to be bought.
How the answers are worked out
The coating identity is the starting point of most pages: paint equals area times coats divided by the spread rate, and the spread rate comes from the product's own tin or data sheet. The ceiling and woodwork pages give the rates their sources report for North American paints and, separately, for UK and European emulsions and glosses, and say the tin is the figure to use. The woodwork page adds that no published standard governs joinery paint quantities, so it applies the identity to door faces and to frames and skirting measured as run times painted girth. The metalwork page measures the same way, by girth, because the brush goes round the section as well as along it.
Each correction has a page of its own. Primer takes a lower spread rate than a topcoat. A mist coat is thinned on the tin's terms, water added as a proportion of the paint, so that twenty per cent means one part water to five parts paint. Over a dark colour the number of coats depends on the contrast ratio of ASTM D2805, which is rarely published for architectural paint, so the coat counts are planning figures, with two coats the practical floor and a tinted primer saving finish coats. Spraying is corrected by transfer efficiency as ASTM D5286 defines it, in bands the page calls planning figures because published values differ with the test method, and the paint that charges the hose is a fixed loss that does not shrink with the job.
Two-pack coatings are limited by pot life more than by the size of the job: the ratio and the pot life come from the data sheet, by volume or by weight, and an off-ratio mix is a defective coating. Paint boxing exists because tint is matched to a tolerance from batch to batch, and it allows for the headroom that mixing needs, so the usable volume is less than the stated size. Intumescent coating is steel surface area times wet film thickness, which is the target dry film thickness divided by the product's solids content.
Units and documents by market
The market setting chooses the system the answers appear in: gallons and square feet for the United States, litres and square metres for the other three markets, each answer restated in the other system. The dew point page checks the margin above the dew point that coating data sheets set, three Celsius degrees or five Fahrenheit, citing an Australian maker's information sheet and an American maker's application guide, with ISO 8502-4 as the guidance for steel. The table shows which documents the other calculators cite for each market.
| Market | Ordered by | Measured as | Worth knowing |
|---|---|---|---|
| United States | Gallons, with the spread rate on the can in square feet per gallon | ASTM D2805 for contrast ratio and ASTM D5286 for transfer efficiency; ASTM D4258 and D4259 are named by the block filler page | Tnemec's application guide is one of the two data sheets behind the dew point margin. |
| United Kingdom | Litres, with UK and European emulsions and glosses rated apart from North American paints on the ceiling and woodwork pages | The spread rates the ceiling and woodwork pages report for UK and European products, in square metres per litre | The two-pack page takes the data sheet's ratio and pot life, so it applies wherever the product is sold. |
| Australia | Litres, with answers restated in the other system | A Wattyl information sheet on application conditions is cited by the dew point page | Few pages here cite an Australian document; the site names the NCC as this market's reference. |
| Canada | Litres, metric first, with answers restated in the other system | ISO 8502-4, as the Standards Council of Canada records it, for the condensation check before coating steel | Provincial and municipal amendments govern over any model code, as the site's own market note says. |
Losses and whole containers
Counts round up to whole containers. The metalwork page says the loss on open metalwork is far higher than on a flat surface, which is why railings have a page of their own; the spray page adds overspray and the hose charge to the quantity that has to end up on the surface; the masking page orders tape by the roll length, rounded up, and sheeting by the sheet. Edges are counted as lengths because tape follows the lines being cut in, plus a length for each frame, which does not scale with the size of the room.
The order the coats go on
The groups follow the work. Conditions come before anything is applied: the dew point margin is checked before a coating goes on cold steel or masonry. Then protection and preparation, masking, floor sheets, block filler and the mist coat on new plaster. Then the primer, then the finish coats, with the coverage over a dark colour deciding how many. The corrections for method and container come last: spray losses, the batch size a pot life allows, and the boxing of tins so that a changeover does not show as a step on the wall.
What the calculators leave to others
Every figure that belongs to a product is an input taken from the tin or the data sheet: the spread rate, the mixing ratio, the pot life and the solids content. The pages that quote a typical spread rate say it varies by product and that the label governs. The tint pages predict no colour; they work in proportions and in the load a base can carry. The floor pages derate a primer's data sheet coverage for a profiled slab, because the rate was measured on a smooth one.
Which calculator for which job
Every paint calculator on the site, grouped by what it does for the material, with the reason it is here. Open the one that matches the question in front of you; each restates its answer in both unit systems.
Rooms, ceilings and woodwork
Walls, ceilings, doors, frames and skirting, with the primer, the first coat on new plaster and the protection that goes with them.
| Calculator | What it does for paint |
|---|---|
| Paint Calculator | The paint a room takes from its dimensions, its doors and windows and the number of coats. |
| Ceiling Paint Calculator | A ceiling's paint from its area, the coats and the spread rate on the tin. |
| Woodwork Paint Calculator | Paint for doors, door frames and skirting from their sizes and runs. |
| Paint Primer Calculator | The primer a surface takes, at primer's own spread rate. |
| Mist Coat Calculator | The paint and the water for a thinned first coat on new plaster. |
| Block Filler Coverage Calculator | The filler an open-textured masonry wall absorbs on its first coat, against the data sheet's smooth-surface rate. |
| Paint Coverage Over Dark Colours Calculator | The coats it takes to cover a dark colour with a light one, and the finish coats a tinted primer saves. |
| Masking and Protection Materials Calculator | Dust sheets, masking tape and floor protection, counted from the edges and the floor. |
Outdoor surfaces and railings
Fences, decks, pavers, drives and metalwork, which take stains, sealers and paint at their own coverage.
| Calculator | What it does for paint |
|---|---|
| Exterior Paint Calculator | The paint a house exterior takes, with the rougher surface's lower coverage allowed for. |
| Deck Stain Calculator | Stain or sealer for a deck, from its area and the coats. |
| Wood Fence Stain Calculator | Stain for a fence from its length, height and the sides coated. |
| Paver Sealer Calculator | Sealer for a patio, walkway or drive of pavers. |
| Asphalt Sealcoat Calculator | Driveway sealcoat for a squeegee-applied job. |
| Metalwork and Railing Paint Calculator | Paint for railings, gates and steelwork from length and girth, because a balustrade has no area to read off. |
Floor coatings and painted lines
Epoxy and its primer on a slab, and the line markings painted on drives, car parks and courts.
| Calculator | What it does for paint |
|---|---|
| Epoxy Floor Coating Calculator | The two-part epoxy kits a garage or basement floor takes. |
| Epoxy Flooring Coating Coverage Calculator | The epoxy a floor needs from its area, the coverage rate and the number of coats. |
| Epoxy Primer Coverage Over a Profiled Slab Calculator | An epoxy primer's coverage reduced for the surface profile of the slab it goes onto. |
| Floor Primer Dilution and Coverage Calculator | The neat primer and the water in a diluted coat, so a mixed coat is bought as the part-tin it is. |
| Line Striping Paint Calculator | Line-striping paint for parking spaces and driveway markings. |
| Sports Court Floor Line Marking Paint Calculator | Paint for the playing lines of a gym or sports court floor. |
Steel and protective coatings
Primer and intumescent coating counted from the surface area of structural members.
| Calculator | What it does for paint |
|---|---|
| Structural Steel Primer Coverage Calculator | Primer or paint for structural steel from the perimeter, length and count of the members. |
| Intumescent Fireproof Coating Volume Calculator | The intumescent coating a target dry film thickness needs on structural steel. |
Mixing, tinting and thinning
Ratios, tint loads and batch sizes for paint that is blended, lightened, darkened or catalysed on site.
| Calculator | What it does for paint |
|---|---|
| Paint Mix Ratio Calculator — Two Paints, Recordable Parts | The volumes of two paints for a chosen ratio, the reduced parts to write on the lid and a sample batch. |
| Paint Tint Ratio and Colourant Load Calculator | The colourant a batch needs for a tint load, and whether the base can carry it. |
| Paint Lightening and Darkening Calculator | The white or tinting black to add for a stated proportion, and why the two directions differ so much in scale. |
| Paint Boxing Calculator — Blending Tins Before You Start | The containers it takes to blend several tins into one colour, and where a changeover falls. |
| Two-Pack Paint and Coating Mixing Calculator — Pot Life and Batch Size | The base and hardener to mix, and the batch size that the pot life allows. |
Conditions and losses
Whether the surface is warm enough to coat, and how much of a sprayed coating reaches the surface.
| Calculator | What it does for paint |
|---|---|
| Dew Point and Relative Humidity Calculator (with the Coating Surface Check) | The dew point and humidity, with the margin above it that coating data sheets set. |
| Paint and Coating Overspray Transfer Efficiency Calculator | How much coating to buy once overspray and the paint left charging the hose are counted. |
Whole jobs, taken off
A job takeoff asks for the dimensions once and returns every line the job needs, each from its own calculator. These are the ones where paint is a main line.
- Repaint a room
A room redecorated: the walls with the openings taken out, the ceiling, and the doors, frames and skirting, with the primer, the dust sheets and the tape.
- Exterior repaint of a house
The outside of a house repainted: masonry paint on the walls, enamel on the joinery and metal paint on railings, with the access, the lead check and the preparation set out as work.
- Garage floor coating
Epoxy kits and coating volume for a concrete garage floor, with self-levelling compound for a floor that has to be made flat.
Read an answer backwards
When you start from what you hold and want to know what it will cover, these pages run the same calculators in reverse.
- How much wall will my paint cover?
- How many ceilings will my paint cover?
- How much wall will my primer cover?
- How much siding will my exterior paint cover?
- How big a deck will my stain cover?
- How much fence will my stain cover?
- How big a patio will my paver sealer cover?
- How long a driveway will my sealer cover?
- How much garage floor will my epoxy cover?
- How much new plaster will my mist coat paint cover?
- How much block wall will my block filler cover?
- How many feet of parking lines will my striping paint cover?
- How much court line will my line marking paint mark?
Worked examples
A job worked through with its inputs and its working shown, so you can see the figures before you enter your own.
- Bedroom repaint
A bedroom repainted from a dark colour to a light one: the protection, the walls, the coats over dark, the primer, the ceiling, the woodwork and the boxing of tins, in the order they are worked.
- A bedroom's walls, in litres of paint
Paint for the walls of a 4 by 3.5 m bedroom, 2 coats
- A living room repainted, in gallons
Paint for the walls of an 18 by 14 ft living room with 9 ft walls
Reference tables
- Production rates by operation
How long each operation takes one person, in person-hours per unit of work.
Guides
The practice behind the numbers: how the work is done, what goes wrong and how to check it.
- Painting Interior Walls
On interior work the substrate sets the numbers: porosity, adhesion and the old colour decide coverage, primer class and coat count.
- Painting Woodwork and Trim
Why a white gloss goes ivory behind the door, what a live knot does to a waterborne film, and how a metre of moulding becomes a square metre of paint.
- Estimating Coatings for Block Walls and Timber Fences
A printed spread rate is measured on a smooth panel; open block and rough-sawn timber break that assumption by factors, not by percentages.
- Laying a Resinous Floor
Resin floors fail at the slab, not the topcoat — read moisture, profile and contamination before any resin is opened.
- Marking Out Lines and Sports Courts
A court is a geometry problem that ends in a spray gun: how to set out, prove and record the lines before any paint is mixed.
- Resealing and Restriping Asphalt
A repaint is an alteration, not housekeeping. Why 244 stalls across two lots owe nine accessible spaces, and what that does to a seal-and-stripe.
- Fire Protecting Steel to Its Section Factor
The period is a property of the building and the thickness is a property of the member. How to build the section factor column the applicator is waiting on.
- Resurfacing a Deck on Its Existing Frame
The frame is the half you inherit. Whether it takes composite at the spacing it already has is a board question first and a joist question second.
Terms
How the numbers are worked out
Every calculator names the method it uses and the standard or guidance behind it. These are the methods the most of the calculators above rest on, and the published documents they cite.
Methods
- Coverage Rate and Spread
How a datasheet figure becomes an order quantity, why it is quoted per coat and calculated for a smooth plane, and what a real substrate does to it. Applies to 17 of the calculators above.
- Quantity, Waste and Rounding
Why a material count is a ceiling function rather than a division, and why the waste factor — not the geometry — carries the risk. Applies to 5 of the calculators above.
- Capacity, Duty Cycle and Dose
Why a lightly loaded generator wastes fuel and damages itself, why a propane tank can be full and still starve an appliance in cold weather, and why a bigger softener uses less salt per litre treated. Applies to 4 of the calculators above.
- Airtightness, Infiltration and Moisture
Why a blower-door result is not an air change rate, why a leak at the top of a house matters far more than the same leak halfway up, and why sealing without ventilating moves the problem rather than solving it. Applies to 1 of the calculators above.
- Nominal Sizes, Land Measure and Setting Out
Why a two-by-four is one and a half by three and a half, why a board foot is a volume the board does not contain, and why checking the diagonals finds an error that measuring the sides cannot. Applies to 1 of the calculators above.
- Rolls, Sheets and the Lap Between Them
Why covering an area with rolls is a strip count rather than a division, why the lap is bought twice over, and why turning the strips the other way can change the order. Applies to 1 of the calculators above.
Frequently asked questions
- How much paint do I need for a room?
- The paint calculator takes the room's dimensions, subtracts its doors and windows and applies the number of coats at the spread rate you enter, which should come from the tin. The ceiling and woodwork calculators count those surfaces separately, and the primer calculator uses primer's own, lower spread rate.
- How many coats does it take to paint over a dark colour?
- The coverage over dark calculator gives planning figures, since the contrast ratio that decides it is rarely published for architectural paint. It treats two coats as the practical floor, and shows how many finish coats a primer tinted toward the topcoat can save.
- What is a mist coat?
- A mist coat is a first coat thinned with water for new plaster. The mist coat calculator splits the quantity into the paint you buy and the water that comes from the tap, using the dilution stated on the tin, where twenty per cent means one part water to five parts paint.
- How much extra paint does spraying use?
- The spray transfer efficiency calculator starts from the quantity that has to end up on the surface, then adds overspray by equipment class, using bands it calls planning figures, and adds the paint that charges the hose, which is a fixed loss that matters most on a small job.
- Can I rely on the spread rate in a calculator?
- Treat it as a starting point. The pages that quote a typical spread rate say it varies by product and surface, and that the rate on your own tin or data sheet is the figure to use. Enter that rate, and the calculators work from it.