Cost to Drywall a 400 Square Foot Basement

The cost to drywall a 400 square foot basement: the math first

Start with the walls. A 400 sq ft basement footprint is commonly close to a 20 ft × 20 ft square, so the perimeter is 2 × (20 + 20) = 80 linear feet. Multiply by an 8-foot ceiling height and the gross wall area is 80 × 8 = 640 square feet. Basements typically have two doors (a main entry and a utility-room door, about 20 sq ft each) and a couple of small basement windows for light (roughly 3 ft × 2 ft, or 6 sq ft, each) — call it two of each for this example. That's 40 + 12 = 52 sq ft of openings, leaving 640 − 52 = 588 square feet of net wall area to actually cover. (If a basement room is used as a bedroom, codes like IRC R310 require a true egress window with at least 5.7 sq ft of net clear opening — reduced to 5.0 sq ft for grade-floor or below-grade openings, which covers most basement egress windows — at least 24 in. high and 20 in. wide, usually a 3×4-ft unit or larger, so swap in that bigger size and subtract its real rough opening before you order.)

Add the standard 10% cutting-waste allowance: 588 × 1.10 = 646.8 square feet. A standard 4 ft × 8 ft sheet covers 32 square feet, so 646.8 ÷ 32 = 20.2, which rounds up to 21 sheets for the walls — you always round up to the next whole sheet, never down. If you also drywall the ceiling, that adds the full 400 sq ft floor footprint: 400 × 1.10 = 440 square feet, and 440 ÷ 32 = 13.75, rounding up to 14 more sheets. Finish both walls and ceiling and the total is 21 + 14 = 35 sheets.

Why basement walls usually need moisture-resistant board

Basement walls sit below grade against a foundation that can wick moisture through the concrete, and standard paper-faced drywall is exactly the kind of material mold grows on when it stays damp. That's why contractors typically spec moisture-resistant (MR, sometimes called "green board") or paperless, fiberglass-faced board for any wall built directly against an exterior foundation wall — interior partition walls that don't touch the foundation can still use standard board.

That protection costs more per sheet. Using representative national price ranges — standard 1/2-inch board around $13 a sheet and moisture-resistant board around $19 a sheet — the 21 sheets needed for our basement's walls come to $273 in standard board versus $399 in moisture-resistant board, a $126 premium for the whole room, or about $6 extra per sheet. That's a small increase next to the cost of tearing out and replacing moldy board a few years later, which is the real reason to pay it even though the finished wall looks identical either way.

Materials cost breakdown: four basement scenarios

Sheet cost isn't the whole materials bill. Joint compound, tape, and screws scale with how much board you actually hang — a standard rule of thumb is about 1 gallon of mud per 100 sq ft, about 12 feet of tape per 4×8 sheet (USG's published figure is roughly 370 ft per 1,000 sq ft), and roughly one screw per square foot, which rounds up to about $0.10 per square foot of installed board. That's about $67 in extras for the 672 sq ft of drywall installed on the walls alone, or $112 once the 448 sq ft ceiling is added. A basement ceiling is often finished in 5/8-inch board (around $16 a sheet) rather than 1/2-inch, mainly for sag resistance where joists are 24 in. on center; a sag-resistant 1/2-inch ceiling board is a lighter alternative at that spacing, and standard 1/2-inch board is usually fine on 16 in. centers. Building code (IRC R302.13) generally only requires a 1/2-inch gypsum membrane under unprotected floor framing such as engineered I-joists, so confirm what your local inspector actually expects before assuming you need the thicker board.

Putting the sheet cost and the extras together gives four realistic materials totals for this basement, plus what a professional installer typically charges for the same job:

• Walls only, standard 1/2-inch board: 21 × $13 = $273 + $67 extras = $340
• Walls only, moisture-resistant board: 21 × $19 = $399 + $67 extras = $466
• Walls (standard) + ceiling (5/8-inch): $273 + (14 × $16 = $224) + $112 extras = $609
• Walls (moisture-resistant) + ceiling (5/8-inch): $399 + $224 + $112 extras = $735
• Installed by a pro, walls only: about $882–$2,058 (588 sq ft × $1.50–$3.50/sq ft, HomeGuide 2026)
• Installed by a pro, walls + ceiling: about $1,482–$3,458 (988 sq ft × $1.50–$3.50/sq ft, HomeGuide 2026) — overhead ceiling work often lands toward the upper end of that range

Where the estimate can move, and how to keep it accurate

The single biggest swing factor is whether you finish the ceiling at all. Many basement remodels skip drywalling the ceiling entirely and install a drop (suspended) ceiling instead, specifically because it leaves the ductwork, plumbing cleanouts, and electrical junctions above it accessible for future repairs — a drywalled ceiling has to be cut open and patched every time a pipe needs attention. If that's your plan, the realistic number for this basement is the $340–$466 walls-only range, not the $609–$735 combined figure.

The second-biggest swing is openings and layout. Every extra interior wall, closet, or bathroom rough-in adds board on both faces of new framing — a partition wall needs drywall on each side, while an exterior wall only needs one — so subdividing a basement increases the sheet count faster than a simple perimeter calculation suggests. Irregular shapes (an L-shaped footprint around a staircase, for example) need to be broken into rectangles and summed rather than treated as one 20×20 box. Before ordering, plug your basement's actual room-by-room dimensions and opening counts into a drywall calculator rather than scaling this example, since a narrower or more subdivided basement can need noticeably more sheets per square foot of floor than an open one.

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