Thickness: Strength and Fire Rating
Thickness is the first decision, and it comes down to what the board has to carry and whether it needs a fire rating.
- 1/2-inch is the everyday standard for interior walls. It is strong enough spanning studs at 16 inches on center, light enough to hang efficiently, and it is what you will use on the large majority of a house.
- 5/8-inch is the heavier board for ceilings (it resists sag overhead) and for fire-rated Type X assemblies. It costs more and weighs more, but on a ceiling or a rated wall it is not interchangeable with 1/2-inch.
- 1/4-inch is thin, flexible board for curves and arches. It bends around a radius that would snap a standard sheet and is often doubled up to regain strength once the curve is formed.
There is also 3/8-inch board, used mostly for re-covering over an existing surface or for some repairs, but 1/2 and 5/8 cover the vast majority of new work.
Board Type: Standing Up to Moisture
The other axis is what the board is made to resist. Ordinary “white” board is fine for dry living space. In rooms with humidity or water you step up:
- Moisture-resistant (green board)— a water-resistant face and core for damp rooms: bathroom walls outside the tub, laundry rooms, utility spaces. It handles humidity, not direct water.
- Mold-resistant (purple)— goes a step further with a mold- and moisture-resistant core and facing, a good choice for bathrooms and basements where humidity lingers.
- Cement board / tile backer — for wet areas: inside shower and tub surrounds behind tile, where water hits the wall directly and repeatedly. This is not gypsum board at all; it will not turn to mush the way even moisture-resistant drywall eventually does in the wet zone.
Type X: Fire-Rated Board
Type Xis fire-rated drywall, almost always in 5/8-inch, with a glass-fiber-reinforced core that holds together longer in a fire so a rated assembly earns its fire-resistance time. Code calls for it in specific places — most commonly the wall (and often the ceiling) between a house and an attached garage, and around certain furnace and mechanical rooms. Where a fire rating is specified, standard board does not pass inspection. If your job includes a garage-to-house wall, put Type X on your list before you order.
Comparison Table
| Board | Where it goes | Why | Relative cost |
|---|---|---|---|
| 1/2″ standard | Interior walls, most of the house | Strong on 16″ studs, light to hang | Baseline |
| 5/8″ standard | Ceilings; wider-spaced framing | Resists sag overhead | Higher than 1/2″ |
| 5/8″ Type X | Garage-to-house wall, rated assemblies, some mechanical rooms | Fire-rated core meets code | Higher — fire-rated |
| 1/4″ flexible | Curved walls, arches, barrel ceilings | Bends to tight radii; often doubled | Similar per sheet; more sheets when doubled |
| Moisture-resistant (green) | Bathroom walls outside the tub, laundry, utility | Handles humidity, not direct water | Above standard |
| Mold-resistant (purple) | Bathrooms, basements, humid rooms | Mold- and moisture-resistant core and face | Above standard |
| Cement board / tile backer | Inside shower and tub surrounds behind tile | True wet-area substrate; will not soften | Highest of the group |
How to Spec a Whole House
Put together, a typical house uses 1/2-inch on the walls, 5/8-inch on the ceilings, 5/8-inch Type X on the garage-common wall, green or purple board on the bathroom and laundry walls, and cement board inside the shower. Sheets are sold in 4×8 (32 sq ft) as standard, with 4×9, 4×10, and 4×12 (48 sq ft)available — longer sheets mean fewer seams to finish, which is worth ordering where your access allows. Because you are mixing board types with different prices, size each area separately: run the numbers on the Drywall Calculator and cross-check the board mix against Drywall Prices by State so the heavier and specialty sheets are priced in, not a surprise. When you are ready to hang it, our drywall installation guide covers the sequence.
Frequently Asked Questions
Should I use 1/2 or 5/8 drywall on my ceiling?
Use 5/8-inch on ceilings. It resists sagging between joists far better than 1/2-inch, which can droop over time, especially on framing spaced wider than 16 inches or where blown-in insulation adds weight above. Many codes and assemblies require 5/8-inch on ceilings for exactly this reason. The heavier board costs a little more per sheet, but it is the right call overhead.
What is Type X drywall?
Type X is fire-rated drywall, almost always 5/8-inch, with a core reinforced by glass fibers that hold together longer in a fire to give a rated assembly its fire-resistance time. It is required in specific locations by code — commonly the wall between a house and an attached garage, and around some furnace and utility areas. Where a fire rating is called for, ordinary board will not pass; you need Type X.
Can I use green board in a shower?
No, not as a tile backer inside the wet zone. Moisture-resistant green board and mold-resistant purple board are for damp rooms — bathroom walls outside the tub, laundry rooms — where there is humidity but not direct, repeated water. Inside a shower or tub surround behind tile you need cement board or another approved tile backer, because green board will eventually fail where water hits it directly.
What thickness of drywall is used for curved walls?
Use 1/4-inch board for curves and arches. It is thin and flexible enough to bend around a radius that would crack thicker board, and it is often doubled up — two 1/4-inch layers laminated together — to reach the strength of a standard sheet once the curve is set. Standard 1/2-inch is too stiff for tight radii.
Related Calculators
- Drywall Calculator — Size the sheet count for each board type by room
- Drywall Prices by State — Compare standard, heavier, and specialty board pricing
- Paint Calculator — Size primer and paint once the board is up and finished
Written by Daniel McCarney — AceCalc