🏡 Decking Calculator

Plan your deck project. Calculate boards, joists, screws, and posts needed for a perfect outdoor space.

Deck Length (ft)

Deck Width (ft)

Board Width

Joist Spacing

Deck Height (inches above ground)

Screws per Board

📊 Your Decking Estimate

Deck Area —

Deck Boards Needed —

Joists Needed —

Support Posts —

You need 0 deck screws

Estimated Cost (materials only) —

How to Plan a Deck Project

Building a deck is a rewarding DIY project, but getting the materials right is critical. Order too little and you'll pay for multiple deliveries; order too much and you waste hundreds of dollars.

Joist spacing: 16" on-center is standard for residential decks. Use 12" spacing for hot tubs or heavy planters.

Materials Checklist

Deck boards: Usually 5/4" × 6" (actual 1" × 5.5")
Joists: 2×8 or 2×10, spaced 16" OC
Ledger board: 2×10 or 2×12, bolts to house wall
Posts: 4×4 or 6×6, concrete footings below frost line
Beams: Double 2×10 or 2×12, supports joist ends
Screws: Use exterior-grade deck screws, ~350 per 100 sq ft

Cost Estimates (2026)

Pressure-treated lumber: $15–25/sq ft installed (basic)

Composite decking: $30–60/sq ft installed (low maintenance)

DIY cost: $10–18/sq ft (materials only)

Related Calculators

Concrete Calculator · Flooring Calculator · Paint Calculator

FAQ

Frequently Asked Questions

How much decking do I need for a 12×12 deck?

A 12×12 ft deck (144 sq ft) needs approximately 155-160 sq ft of decking boards (including 10% waste). This equals about 50-55 12-ft boards (5.5″ wide). Use our calculator for exact estimates.

How far apart should joists be?

16″ on-center (OC) for residential decks (standard). 12″ OC for hot tubs or heavy loads. 24″ OC is allowed for some composite decking (check manufacturer specs).

What's the best decking material for DIY?

Pressure-treated pine is cheapest ($2-4/sq ft) and DIY-friendly. Composite (Trex, TimberTech) costs more ($6-10/sq ft) but needs zero maintenance. Cedar/redwood look great but need annual sealing.

How many deck screws do I need?

Use 2 screws per joist intersection (top + bottom). For a 12×12 deck, you'll need ~350-500 screws (1-1.5 lbs). Buy ceramic-coated exterior screws (never use drywall screws outdoors).

Do I need a permit for a deck?

Most cities require permits for decks over 30″ high or attached to the house. Check local building codes before starting. Permits cost $200-500 but protect you if you sell the house later.