Primer calculator: how much primer do I need?
Primer goes on once, usually, and how far it spreads depends on what it is sealing. New drywall is planned at the 400 sq ft per gallon on drywall-primer data sheets; stains, bare wood and masonry at less.
Enter your measurements
More options: Door · Window · Coverage …
- Primer needed
- 0.84 gal (3.16 L)
- Cans of the size you chose
- 1 can · 1-gallon
- Area primed (one coat)
- 334 sq ft
- Primer per coat
- 0.84 gal
- Coverage used
- 400 sq ft/gal
2 × (12 ft + 12 ft) × 8 ft = 384 sq ft of wall − 1 door × 20 sq ft − 2 windows × 15 sq ft = 334 sq ft
334 sq ft × 1 coat ÷ 400 sq ft/gal = 0.84 gal → buy 1 gallon
- Using a planning coverage for this surface from the data sheets. Your primer’s label is the better number.
- New drywall needs primer even under “paint and primer” products: bare paper and joint compound absorb differently, and without primer the joints show through as dull or shiny stripes.
- Old house? If it was built before 1978, read lead paint safety before you sand or scrape: EPA advises assuming old paint contains lead until it is tested.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much primer for a 12x12 room | 0.84 gal: buy 1 gallon |
| How many gallons of primer for 1,000 sq ft of new drywall | 2.5 gal: buy 2 gallons + 2 quarts |
Primer for this area by surface
| Surface | Primer needed | Buy (gallons and quarts) |
|---|---|---|
| new drywall | 0.84 gal | 1 gallon |
| color change, dark to light | 0.84 gal | 1 gallon |
| stains or glossy paint | 1.34 gal | 1 gallon + 2 quarts |
| bare wood | 1.34 gal | 1 gallon + 2 quarts |
| masonry or stucco | 1.67 gal | 2 gallons |
Pick a room or type an area, then the surface. The planning coverage for each surface comes from a manufacturer’s data sheet; type your primer’s own figure under More options to override it. New to this? Paint words explained.
How much primer: the formula
primer = area × coats ÷ coverage new drywall: 400 sq ft/gal (9.8 m²/L) stain-blocking or bare wood: 250 sq ft/gal · masonry: 200 sq ft/gal
Where the planning figures come from
| Surface | Planning figure | Data sheet |
|---|---|---|
| New drywall | 400 sq ft/gal | Sherwin-Williams ProMar 200 Zero VOC Interior Latex Primer: 400 sq ft/gal at 4 mils wet. USG’s drywall estimating table also assumes 400 for its First Coat primer. |
| Color change, dark to light | 400 sq ft/gal | A regular primer tinted toward the new color, at the same 400 sq ft/gal as on drywall (Sherwin-Williams ProMar 200 primer). |
| Stains, patches, glossy paint | 250 sq ft/gal | Behr Multi-Surface Stain-Blocking Primer No. 436: 250–400 sq ft/gal depending on method and porosity (low end used). |
| Bare wood | 250 sq ft/gal | Same Behr range; end grain and rough-sawn boards soak up the most. |
| Masonry, brick, stucco | 200 sq ft/gal | Sherwin-Williams Loxon Concrete & Masonry Primer: 200–300 sq ft/gal; about 80 on porous, rough stucco. |
Worked examples
- How much primer for a 12x12 room: new drywall, walls only and with the ceiling.
- How many gallons of primer for 1,000 sq ft of new drywall: about 31 sheets of 4 × 8, the scale of a basement or addition.
When you need primer, and when you don’t
- Always: new drywall and joint compound, bare wood, patches larger than a nail hole, water and smoke stains, and anything glossy (scuff it first).
- Usually: big color changes. Going from dark to light, one coat of tinted primer over the whole wall (choose Color change above) usually saves a finish coat; under deep colors, a gray- or color-tinted primer does the same.
- Often not: a sound, clean, previously painted wall getting the same or a similar color. Two coats of paint do the job.
- Stain-blockers: water, smoke, marker and knots in pine need a stain-blocking primer. A regular PVA drywall primer won’t stop them bleeding through.
Tips
- Ask the store to tint the primer toward your finish color. It won’t change coverage, but it can save a finish coat.
- Prime before the final sanding of patches? No: sand the mud first, wipe off the dust, then prime. Primer shows up remaining flaws so you can fix them before the color goes on.
- On new drywall, a primer that equalizes absorption between paper and mud is what stops joints “flashing” through an eggshell finish.
Hanging the drywall first? How many sheets of drywall for a 12x12 room and how much mud per sheet cover the board and the joints.
What you’ll need
- PVA drywall primerBudget price
Seals bare paper and mud so the finish coat dries evenly. Data sheets for most wall paints call for it on new drywall.
See options on Amazon (opens in a new tab) - Paint roller frame and covers (9 in)Budget price
A sturdy 9 in frame and a few 3/8 in nap covers handle smooth drywall. Rougher walls and ceilings want 1/2–3/4 in nap, as the data sheets suggest.
See options on Amazon (opens in a new tab) - Sanding sponges (fine/medium)Budget price
Knocks down patches and scuffs glossy trim so the next coat grips. Damp sponges keep dust down.
See options on Amazon (opens in a new tab) - Paint tray and linersBudget price
Liners turn a color change or the end of the day into a two-minute job instead of a scrub at the sink.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much primer do I need for new drywall?
At the 400 sq ft per gallon on drywall-primer data sheets, about a gallon per 12 sheets of 4 × 8. 1,000 sq ft of board takes 2.5 gallons: see primer for 1,000 sq ft of new drywall.
How many coats of primer does drywall need?
One, followed by two coats of finish paint, is the system on most data sheets. A second coat of primer is only needed if the first shows dull and shiny patches over the joints.
Do I need primer if my paint has primer in it?
On new drywall, bare wood and stains, yes. Paint-and-primer products are designed to cover previously painted walls in fewer coats; their own data sheets still list a separate primer for new drywall.
How much primer for a 12x12 room?
About 0.84 gallons for the walls of new drywall with a door and two windows out, so one gallon; with the ceiling, a gallon and a quart. See how much primer for a 12x12 room.
Does primer cover as far as paint?
On drywall it often goes further (400 sq ft per gallon vs 350–400 for paint), because it is thinner. On porous masonry and bare wood it goes much less far.
Related guides
Sources
- Sherwin-Williams, ProMar 200 Zero VOC Interior Latex Primer (B28W02600), product data sheet (opens in a new tab) — Coverage 400 sq ft per gallon at 4 mils wet; one coat on drywall, then two finish coats.
- USG, How to Install and Finish Sheetrock Brand Gypsum Panels (J371) (opens in a new tab) — Panel coverage table; per 1,000 sq ft of panels: 2.7 lb of Type W screws (12 in on ceilings, 16 in on walls), 5.3 lb of nails, 370 ft of joint tape, about 10 gal of All Purpose or 9 gal of Plus 3 compound; First Coat primer at 400 sq ft/gal.
- Behr, Multi-Surface Interior/Exterior Stain-Blocking Primer & Sealer (No. 436), technical data sheet (opens in a new tab) — Coverage 250–400 sq ft per gallon depending on application method and porosity.
- Sherwin-Williams, Loxon Concrete & Masonry Primer/Sealer (A24W8300), product data sheet (opens in a new tab) — Coverage 200–300 sq ft per gallon; about 80 sq ft per gallon on porous, rough stucco.
- US EPA, Renovation, Repair and Painting Program: Do-It-Yourselfers (opens in a new tab) — Assume pre-1978 paint has lead unless tested; contain the area, mist before sanding, HEPA vacuum, N-100 respirator, wet cleanup.