Understanding your result
The headline is the number of coats of finish paint, and the sub-line names the primer that goes under them, or says none is needed. The three figures show whether a primer is used, the paint compared with a standard two-coat job (× 1.5 for three coats, × 0.5 for a refresh) and the finish paint for the area if you entered one.
The table restates the case (from, to, surface), the coats, the primer with its type, the multiplier and, with an area, the finish paint and the primer in gallons and cans. The “Why” panel lists the rules that decided it, one per line, so a recommendation can be checked against your own situation rather than taken on trust.
This is the calculator to run before the quantity calculators, because their default of two coats is right only most of the time. The primer calculator takes the primer type this one names and gives the quantity for a whole room; the accent wall calculator applies the same depth rules to a single feature wall; and the wall paint calculator takes the number of coats as its input.
How we calculate this
The colour scale has five steps: white, light, medium, dark and very dark or saturated. A jump counts as big when it crosses from the two lightest to the two darkest, in either direction, and saturated colours count as big whatever they cover. The surface comes first: a stain blocker, a bonding primer or a drywall primer is required whatever the colours, and when the colours call for a tinted primer too, one primer does both jobs, tinted.
The rules follow the manufacturers’ published guidance on coats and primers and the light reflectance values behind the colour classes, which the dark colours and LRV guide explains. The primer is costed at 300 sq ft per gallon and the paint at your coverage, the figures on the coverage rates table. The coats guide has the whole decision table with sheen changes added.
The assumptions behind the numbers
| Assumption | Rule or default | Where it comes from |
|---|---|---|
| Colour change | 2 coats | Manufacturers’ recommendation on interior paint data sheets |
| Same colour, sound paint | 1 coat | The same guidance for a refresh |
| Big jump or saturated colour | tinted or high-hide primer + 2 coats, or 3 coats | Manufacturers’ guidance for deep bases and colour changes |
| Patched walls | spot primer, about 15% of the area | Site estimate of the patched share |
| Bare, stained, glossy | drywall, stain-blocking or bonding primer | Primer manufacturers’ surface guidance |
| Primer coverage | 300 sq ft per gallon | High-hide and stain-blocking primer data sheets: 300–400 |
| Paint coverage | 350 sq ft per gallon | Interior wall paint data sheets: 350–400 |
| Allowance | 5% | Roller and tray loss |
Assumptions last reviewed October 8, 2026.
The rules are the usual outcome, not a promise for every can. A premium paint with high hide may cover a jump in two coats where a budget line takes three, and some colours mixed in a white base hide better than their depth suggests. The calculator does not model sheen changes on their own; going from gloss to flat over sound paint needs a scuff-sand rather than extra coats, which is what the glossy surface setting covers. A test patch is the final word.
Two worked examples
Light grey walls going navy
Previously painted, sound walls, 350 sq ft, paint at 350 sq ft per gallon, tinted primer used.
- Rule: light to dark, so a primer tinted toward the new colour and 2 coats
- Paint: 350 ÷ 350 × 2 × 1.05 = 2.1 gallons, buy 2 gallons + 1 quart
- Primer: 350 ÷ 300 × 1.05 = 1.23 gallons, buy 1 gallon + 1 quart
Without the primer the rule is three coats, 3.15 gallons of navy: a gallon more of the expensive deep-base paint to save a gallon and a quart of cheaper primer.
A dark red room going white, with patches
Dark to white over patched walls, primer used, same area.
- Rule: dark to light, so a high-hide primer, and because the whole wall is being primed for the colour, the patches are covered too
- Coats: 2 over the primer; paint 2.1 gallons, primer 1.23 gallons
A same-colour refresh of sound walls is the other end of the scale: one coat, 1.05 gallons, no primer. Stained walls going to a medium colour need a stain-blocking primer whatever the other answers are, because stains bleed through any number of coats of ordinary paint.
Where to find your inputs
Colour now and new colour. Hold the paint chip against the wall. The chip or the store’s colour tool usually gives the light reflectance value: above about 60 is light, 20 to 60 medium, under 20 dark, under 10 or any intense red, yellow or orange very dark.
Same colour. Tick only if it is genuinely the same colour, the same product line and the same sheen.
Surface. Look for patches (dull or white spots), stains (yellow or brown rings), gloss (water beads, a fingernail slides) and bare drywall or wood.
Area and coverage. From the square footage or wall paint calculators, and the can.
Common mistakes
- Planning one coat for a colour change. Two is the minimum; the second coat is what makes the colour even.
- Using extra coats instead of a stain blocker. The stain comes back through all of them.
- Untinted primer under a deep colour. White primer under navy is a third coat waiting to happen.
- Skipping primer on bare drywall. The seams flash through every coat.
- Judging coverage while the paint is wet. Wet paint looks darker and more opaque; check it dry, in daylight.
- Thinning to stretch a coat. It lowers the hide and adds a coat.
Questions people ask
- How many coats of paint do I need?
- Two for any colour change, which is the default on every calculator on this site. One only for a same-colour refresh over sound paint. Three, or two over a tinted primer, for a jump from light to dark, from dark to light or to a saturated red, yellow or orange.
- Does primer count as a coat?
- No. Primer seals and evens the surface and, when tinted, gives the paint a closer colour to hide. The finish coats go on top. One coat of a tinted primer usually replaces the third coat of finish paint and costs less.
- Is one coat ever enough?
- For the same colour over sound, clean paint, yes, which is the refresh case. Paints sold as one-coat are formulated to hide well, but even they are rated for one coat only over a similar colour; a colour change still needs two.
- How many coats to cover a dark colour with white?
- Two coats over a high-hide primer, or three without. Dark pigment ghosts through white more than the other way round, and the primer is the cheaper way to stop it. The dark colours guide explains why with light reflectance values.
- Why do red and yellow need extra coats?
- Saturated reds, yellows and oranges are made with transparent, intense pigments in a clear or deep base with little white in it, so each coat hides less. A grey-tinted primer under them is standard practice and saves a coat.
- Do I need primer on a previously painted wall?
- Not if it is sound and the colour change is modest. Patches need spot priming, stains need a stain blocker, gloss needs a bonding primer, and a big colour jump is cheaper with a tinted primer. Otherwise two coats of a good paint do the job.