20' x 24' Deck Material Calculator
A 480-square-foot premium deck approaching a small room addition in scale. This size supports full outdoor kitchens, multiple seating areas, and dedicated space for features like fire pits or hot tubs. This 480 sq ft deck requires approximately 94 standard 5.5" x 12' pressure-treated boards, 16 joists, and 16 support posts.
Material Cost Comparison by Decking Type
The table below compares total material costs for a 20' x 24' deck across eight popular decking materials. All estimates use 16-inch joist spacing, perpendicular board pattern, railing on three sides, and one set of stairs. The structural framing (joists, beams, posts, concrete, hardware) is the same regardless of the surface decking material; only the board cost varies between options.
| Decking Material | Boards | Board Cost | Total Materials |
|---|---|---|---|
| Pressure-Treated Pine | 94 | $2,256 | $9,060 |
| Composite | 94 | $5,076 | $11,880 |
| Composite | 94 | $7,896 | $14,700 |
| Western Red Cedar | 94 | $5,076 | $11,880 |
| Redwood | 94 | $9,024 | $15,828 |
| Ipe Hardwood | 94 | $10,152 | $16,956 |
| Mahogany | 94 | $7,332 | $14,136 |
| PVC | 94 | $6,768 | $13,572 |
Complete Material Breakdown (Pressure-Treated Pine)
The following table provides a complete bill of materials for a 20' x 24' deck using pressure-treated pine 5.5" x 12' decking boards. This represents the most common and affordable configuration for residential decks of this size. Each line item includes the quantity needed and estimated cost at current retail pricing.
| Material | Specification | Quantity | Est. Cost |
|---|---|---|---|
| Decking Boards | 5.5" x 12' PT Pine | 94 boards (1128 lf) | $2,256 |
| Joists | 2x10 pressure-treated | 16 joists (384 lf) | $614 |
| Beams | 2x10 doubled pressure-treated | 4 beams (160 lf) | $256 |
| Posts | 6x6 x 8' pressure-treated | 16 posts | $2,816 |
| Concrete | 60lb bags for footings | 32 bags | $192 |
| Deck Screws | #10 x 3" coated | 5 boxes (1680 screws) | $275 |
| Hardware | Joist hangers & bolts | 16 hangers, 32 bolts | $136 |
| Railing | Posts, rails, balusters | 68 lf (13 posts) | $2,380 |
| Stairs | Stringers & treads | 3 stringers, 4 treads | $135 |
| Total Material Cost | $9,060 | ||
| Professional Labor Estimate (~$25/sq ft) | $12,000 | ||
Board Pattern Comparison
The board-laying pattern affects both the visual appearance of your deck and the amount of material needed. More complex patterns require additional waste allowance due to the angled and mitered cuts involved. The table below shows how pattern choice affects board count and decking cost for a 20' x 24' deck using pressure-treated pine.
| Pattern | Boards Needed | Linear Feet | Board Cost |
|---|---|---|---|
| Perpendicular (10% waste) | 94 | 1128 lf | $2,256 |
| Diagonal (15% waste) | 99 | 1188 lf | $2,376 |
| Herringbone (20% waste) | 103 | 1236 lf | $2,472 |
Planning a 20' x 24' Deck
A 20' x 24' deck provides 480 sq ft of outdoor living space. At this size, you are building a substantial outdoor living area that rivals the size of many indoor rooms. Decks of this magnitude benefit from professional design to optimize the layout, may require engineering review for structural adequacy, and often incorporate features like built-in seating, planter boxes, pergolas, or outdoor kitchen islands. The investment in quality materials pays dividends at this scale because the large surface area amplifies the visual and tactile impact of your material choice.
For a deck of this size, the structural framework requires 16 joists (2x10 lumber, 384 linear feet total), 4 doubled beams spanning the 20-foot width, and 16 support posts set in concrete footings. Because the joist span is 24 feet, which exceeds 12 feet, 2x10 joists are recommended to prevent deflection and ensure a solid feel underfoot.
The total material cost for this deck ranges from approximately $9,060 using pressure-treated pine to $13,572 with premium decking materials. Professional installation adds approximately $12,000 at a typical rate of $25 per square foot. Many homeowners choose to DIY the construction to save on labor costs, which is feasible for experienced builders with this size deck, though permits and inspections may still be required by your local jurisdiction.
Frequently Asked Questions
How many boards do I need for a 20' x 24' deck?
For a 20' x 24' deck (480 sq ft), you need approximately 94 boards using standard 5.5" x 12' pressure-treated lumber with a perpendicular pattern (10% waste factor). If you choose a diagonal pattern, increase that to about 99 boards, or 103 boards for a herringbone pattern. The exact count varies by board length and width; longer boards mean fewer pieces but potentially more waste on cuts.
How much does a 20' x 24' deck cost to build?
Material costs for a 20' x 24' deck range from approximately $9,060 with pressure-treated pine to $13,572 with premium materials like ipe or PVC, including framing, hardware, railing, and stairs. Adding professional labor at approximately $25 per square foot brings the total installed cost to between $21,060 and $25,572 depending on material choice and local labor rates.
What joist size should I use for a 20' x 24' deck?
For a 20' x 24' deck with joists spanning 24 feet, use 2x10 joists at 16 inches on center. 2x10 joists are recommended because the span exceeds 12 feet. You will need 16 joists totaling 384 linear feet. Always use pressure-treated lumber for structural components and verify your local building code requirements.