How this calculator works. Identical room geometry to our paint calculator (perimeter × height, minus standard door/window areas), divided by primer coverage. Rates follow typical manufacturer labels (Kilz, Zinsser): 300 sq ft/gal on sealed surfaces, 225 on bare drywall (its paper face is absorbent), and 200 as a working rate when stain-blocking over marks or dark colors, where a second coat is often the honest answer.
Do you even need primer?
Half the primer sold is unnecessary, and half the paint failures come from skipping it — the trick is knowing which half you're in. You genuinely need primer over: bare drywall or fresh joint compound (they drink paint unevenly and flash-mark forever), stains from water, smoke, or markers (use a stain-blocking primer, or the stain bleeds through five coats of paint), glossy surfaces (bonding primer), raw wood (tannins bleed, especially cedar and redwood), and dramatic color changes (tinted primer saves a whole coat of expensive paint).
You can skip primer when repainting a similar color over sound, matte, previously painted walls — modern paint-and-primer-in-one products are legitimate exactly there, and only there.
Match the primer to the problem
| Situation | Primer type |
|---|---|
| New drywall / fresh mud | PVA drywall primer (cheapest works) |
| Water, smoke, marker stains | Stain-blocking (shellac for the worst) |
| Glossy paint, cabinets, laminate | Bonding primer |
| Dark-to-light color change | Primer tinted toward the new color |
Buying tips
Ask the paint desk to tint your primer gray or toward your finish color for color changes — it's free and can turn three finish coats into two. Primer doesn't need to look pretty, just uniform: even, dull coverage is done.
Common questions
Is paint-and-primer-in-one real?
It's thicker paint with better adhesion — real for repainting sound surfaces in similar colors, not a substitute for true primer on bare drywall, stains, or gloss. The can's marketing skips that footnote.
How long before I can paint over primer?
Most latex primers recoat in 1–3 hours; shellac in under an hour. But don't wait too long either — many bonding primers want topcoat within days or a week for best adhesion. The can's fine print has both windows.
Should primer be sanded?
On trim, cabinets, and anywhere sheen matters: a light scuff with 220-grit between primer and paint noticeably improves the finish. On walls: only sand down ridges or drips.
Can I use leftover primer as paint?
No — primer chalks, marks, and yellows without a topcoat. It's an undercoat by chemistry, not just by name.