Plywood Calculator — Sheets & Cost Estimator

How to Calculate Plywood for Your Project

Whether you're sheathing a roof, building a subfloor, or making cabinets, getting the right amount of plywood saves money and trips to the lumber yard. Each standard plywood sheet is 4 feet × 8 feet (32 square feet). Divide your total area by 32, add waste, and round up.

Plywood Price Comparison (2026, per 4×8 sheet)

Grade	1/4"	3/8"	1/2"	5/8"	3/4"	1"
CDX (construction)	$18	$24	$32	$38	$45	$62
Sanded (A/B, B/C)	$28	$35	$45	$52	$60	$82
Marine Grade	$55	$68	$85	$98	$115	$155
OSB	—	$16	$22	$26	$32	—

Plywood Thickness Guide — Which to Use

Thickness	Common Uses	Max Joist/Stud Spacing
1/4" (6mm)	Cabinet backs, drawer bottoms, paneling, underlayment	Must be glued to substrate
3/8" (9mm)	Wall sheathing, light shelving, craft projects	16" on center
1/2" (12mm)	Shelving, cabinet sides, wall sheathing, underlayment	16" on center
5/8" (15mm)	Roof sheathing, subfloor (light-duty), heavy shelving	24" on center
3/4" (18mm)	Subfloors, workbenches, cabinets, structural use	24" on center
1" (25mm)	Heavy-duty countertops, industrial shelving, specialty	32"+ on center

CDX vs Sanded vs Marine — How to Choose

CDX plywood is the workhorse of construction. The "C" and "D" refer to face grades (C is the better side, D is rougher), and "X" means exterior-rated glue. Use it for anything behind walls or under floors — subfloors, roof sheathing, wall sheathing. It's not pretty, but it's strong and cheap.

Sanded plywood (cabinet-grade) has at least one smooth face. A/B grade means one near-perfect side (A) and one decent side (B). Use it for visible applications: cabinets, shelving, furniture, built-ins. It takes paint and stain beautifully.

Marine plywood is the premium choice. It uses waterproof adhesive (not just water-resistant like CDX) and has void-free cores — no gaps or knotholes in the inner plies. This makes it ideal for boat building, outdoor furniture, docks, and anything permanently exposed to moisture. It costs 2–3× more than CDX.

OSB vs Plywood — Which Is Better?

OSB (oriented strand board) is made from compressed wood strands bonded with resin. It's cheaper than plywood and has more uniform strength because it doesn't have knots or grain direction. However:

• OSB absorbs more moisture and swells along edges. Once wet, it takes much longer to dry than plywood.
• For roof and wall sheathing, OSB is perfectly acceptable and meets all building codes. Most new construction uses OSB here.
• For subfloors, plywood is generally better — especially in kitchens, bathrooms, and basements where moisture is a risk.
• OSB is NOT available in 1/4" or 1" thicknesses. Common sizes are 7/16", 1/2", 5/8", and 3/4".
• Price advantage: OSB typically costs 15–30% less than equivalent CDX plywood.

Pro Tips for Buying Plywood

1. Always overestimate slightly. Running out mid-project means a trip to the store and possibly a different dye lot. 10% waste factor covers most projects.
2. Check sheets for warping before buying. Sight down the edge like a rifle — any twist or bow means rejected cuts and wasted material.
3. Actual thickness is smaller than nominal. A "3/4-inch" sheet is really 23/32" (about 18mm). This matters for joinery and dado cuts.
4. Buy in bulk for discounts. Most lumber yards offer 5–10% off orders of 10+ sheets.
5. Have sheets delivered for large orders. Delivery costs $50–$100 but saves your back and car — a single 3/4" sheet weighs 60–70 lbs.
6. Store flat, not on edge. Leaning plywood against a wall causes it to warp within days.