The short answer
Priming 300 sq ft with one coat at 250 sq ft per gallon takes 1.2 gallons: buy 1 gallon + 1 quart, about $45 (two gallons would be $60).
Starting points by surface
- New drywall: one coat of drywall primer evens out the porous surface.
- Glossy surfaces: a bonding primer helps paint grip after a light sanding.
- Dark to light: primer cuts coats. PaintCare notes a very dark to very light change may take three or even four coats, and a gray or tinted primer can reduce them.
- Stains: use a stain-blocking primer; stubborn stains may need two coats.
These are starting points. Primer coverage varies by product, so type the number from your can.
FAQ
How much primer do I need?
Area × coats ÷ coverage. For 300 sq ft, one coat, at 250 sq ft per gallon, that is 1.2 gallons.
Does primer cover more or less than paint?
Labels vary. We default to 250 sq ft per gallon for primer, a bit less than paint, and you can change it.
Do I always need primer?
No. See our guide on whether you need primer for new drywall, stains, glossy surfaces and big color changes.
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