Technical Free

Primer Calculator

Estimates primer required based on surface type, condition, and coverage. Recommends primer type by surface condition to prevent costly callbacks.

Results

Primer Needed
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gallons
Coverage Rate
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sq ft/gal
Cans Needed
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Est. Cost
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Primer Recommendation

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Coverage rates based on manufacturer data. Actual coverage varies by product, application thickness, and surface porosity. Always check the can label.

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How to Use This Calculator

1. Enter the area to prime. This is the total square footage that needs primer. Not all surfaces in a room may need priming.

2. Select surface type. The surface determines the appropriate coverage rate. Porous surfaces like new drywall and masonry absorb more primer.

3. Choose primer type. The calculator adjusts coverage based on the primer-surface combination. It also provides a recommendation for the best primer for your situation.

4. Set coats needed. One coat handles most situations. Two coats for severe stains, water damage, or glossy surfaces needing extra adhesion.

Primer Coverage by Surface Type

New drywall + latex primer: 300 sq ft/gal

Painted drywall + latex primer: 325 sq ft/gal

Wood + latex primer: 300 sq ft/gal

Masonry + latex primer: 200 sq ft/gal

Metal + oil-based primer: 250 sq ft/gal

Water-stained + stain-blocker: 250 sq ft/gal

Glossy surfaces + bonding primer: 275 sq ft/gal

The calculator includes a 0.5 gallon safety margin to account for touch-ups and uneven application. Primer coverage is generally lower than paint because primer must seal and bond to the substrate.

Frequently Asked Questions

How much primer do I need?
Divide your total area by the primer coverage rate for your surface type. New drywall with latex primer covers about 300 sq ft/gal. Masonry drops to 200 sq ft/gal. Add a 0.5 gallon safety margin for touch-ups. A typical 12x10 room with 8-ft ceilings needs about 1.5 gallons of primer for one coat.
Do I always need primer before painting?
Not always, but primer is recommended for new drywall, bare wood, masonry, stain coverage, color changes from dark to light, and glossy surfaces. If you are painting over a similar color on already-primed drywall, a quality paint-and-primer-in-one may be sufficient.
What primer should I use for water stains?
Use a stain-blocking primer like Zinsser B-I-N (shellac-based) or KILZ Original (oil-based) for water stains. These primers seal the stain and prevent bleed-through. Latex primers are not effective against water stains. Apply one coat, let dry, then check for bleed-through before painting.
How many coats of primer do I need?
One coat is sufficient for most surfaces. Apply two coats when covering severe stains, water damage, smoke damage, or when transitioning from a very dark color to white or light. Also use two coats on glossy surfaces to ensure proper adhesion for the topcoat.

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