Decking Calculator Materials. Deck calculations require board coverage and joist spacing. Formula: Boards equals Deck Area divided by Board Coverage. Standard board: 5.5 inch actual width (sold as 6 inch) covers 0.458 sq ft per linear foot. Example 12×16 ft deck: 192 sq ft divided by 0.458 equals 419 linear feet of 6-inch boards. Add 15 percent waste equals 482 feet. At 12-foot lengths: 41 boards needed. Costs: Pressure-treated pine 2-4 per sq ft, cedar 4-8 per sq ft, composite 6-12 per sq ft, PVC 8-15 per sq ft. Total installed 25-45 per sq ft including framing. Joist spacing determines strength: 12-inch on-center for composite, 16-inch standard for wood, 24-inch for thick boards only. Calculate joists: Deck length divided by spacing plus 1. 16-foot deck at 16-inch spacing: 16 divided by 1.33 equals 12 plus 1 equals 13 joists. Framing lumber: Joists 2×8 or 2×10 treated. Beams 2×10 doubled or tripled. Posts 4×4 or 6×6 pressure-treated. Ledger board 2×8 bolted to house. Joist hangers metal connectors 2 each. Post concrete one 50-pound bag each. Costs per linear foot: Joists 2×8 1.50, 2×10 2.00. Beams 2×10 2.00 doubled. Posts 4×4 7-12 each, 6×6 15-25 each. Railing calculation: Linear feet of rail times components. Standard rail system: top and bottom rails, balusters every 4 inches, posts every 6 feet. Cost 25-100 per linear foot installed. Cable rail 75-200, glass panels 150-300 per linear foot. Example 12×16 deck needs 56 feet railing: mid-grade at 50 per foot equals 2,800. Stairs calculation: Number of steps times tread width. Standard step: 10-inch tread, 7-inch riser. 36-inch rise needs 5 steps. Cost 100-300 per step installed. Stringers (structural support) 2×12 boards, need 3 per 36-inch wide stair. Landing at bottom adds 50-200. Fascia and trim: Cover joist ends with 1×8 fascia board. Calculate deck perimeter. Cost 2-4 per linear foot material. Example 56 feet at 3 equals 168. Deck size affects cost per sq ft: 10×10 deck (100 sq ft) costs 35-50 per sq ft due to fixed costs. 12×16 deck (192 sq ft) costs 30-40 per sq ft. 16×20 deck (320 sq ft) costs 25-35 per sq ft. Larger decks more economical per square foot. Material comparison: Pressure-treated economical, requires yearly sealing, splinters, 15-20 year life. Cedar naturally rot-resistant, beautiful, expensive, 20-25 years. Composite never splinters, low maintenance, hot in sun, 25-30 years. PVC highest cost, coolest surface, never fades, 30-50 years. Each has pros and cons. Fasteners: Deck screws 3-inch coated 8-12 per square foot. Hidden fasteners for composite 20-30 per square foot of boards, cleaner appearance no visible screws. Joist hangers 2 each. Post brackets 10-20 each. Lag bolts for ledger 5-10 each. Common mistakes: Not accounting board waste for cutting, add 15 percent minimum. Forgetting joist framing materials costs equal decking boards. Ignoring railing can double total project cost. Wrong joist spacing causes bounce, check code and manufacturer specs. Measuring in feet but buying by piece lengths, boards come in 8, 10, 12, 16 foot lengths, minimize cuts. Not planning for drainage, deck should slope away from house 1/8 inch per foot. Pro tips: Use joist tape over joists prevents rot at contact points. Composite requires special saw blade and screws. Pre-drill holes prevents splitting near board ends. Stagger board ends not all same joist looks better. Leave 1/8-inch gap between boards for drainage and expansion. Install boards bark-side up prevents cupping. Design features: Built-in benches add 500-1,500. Pergola shade 2,000-6,000. Under-deck ceiling system 10-15 per sq ft. Deck lighting 500-2,000. Skirting encloses under deck 5-15 per linear foot. Each feature adds functionality and cost. Foundation and posts: Deck over 30 inches high needs permit and engineered footings. Frost line depth varies by region 24-48 inches. Dig holes below frost line prevents heaving. Space posts 8-10 feet maximum. Use post-to-beam brackets not toenails. Codes and permits: Deck permit 150-500 required for most builds. Inspections at footing, framing, final stages. Setback from property line usually 5-10 feet. Height over 30 inches needs railing 36-42 inches high. Balusters maximum 4-inch spacing prevents child falling through. FAQ: How much for 12×12 deck? 144 sq ft costs 3,500-6,500 installed depending on materials and features. Treated vs composite? Composite costs double upfront but lasts longer, no maintenance. Can I DIY deck? Yes if experienced, requires multiple tools, heavy materials, building knowledge. Permit needed? Usually yes for attached decks or over 200 sq ft. How long to build? Professional 3-5 days for average deck. DIY 2-3 weekends.