Deck Design Calculator
Decking and Railing Are Two Separate Line Items
A deck quote that only covers square footage is missing a real cost driver: railing is priced by the linear foot, not the deck's footprint, and a small elevated deck with a full perimeter railing can spend nearly as much on rails as on decking. Keeping the two calculations separate, then adding them, produces a far more accurate total than a single blended per-square-foot number.
The Formula
Deck Area = Length × Width
Total Cost = (Deck Area × Cost per sq ft) + (Railing Length × Railing Cost per ft)
Total Cost = (Deck Area × Cost per sq ft) + (Railing Length × Railing Cost per ft)
Where This Calculation Matters
- Comparing decking materials — pressure-treated lumber, composite, and hardwood carry very different per-square-foot costs; running each through the same formula isolates the material cost difference from labor.
- Budgeting elevated decks accurately — a deck more than 30 inches off grade typically requires railing on all open sides, a cost easy to underestimate if only the decking surface is priced.
- Sizing a deck to a budget — working the formula backward from a target total cost helps determine the maximum affordable deck dimensions.
- Planning phased construction — decking and railing can be budgeted and purchased separately, useful for a project completed in stages.
A Worked Example
A 16 ft × 20 ft deck at $35/sq ft in decking material, with 72 ft of railing at $18/ft:
| Item | Calculation | Cost |
|---|---|---|
| Deck area | 16 ft × 20 ft | 320 sq ft |
| Decking material | 320 sq ft × $35/sq ft | $11,200.00 |
| Railing | 72 ft × $18/ft | $1,296.00 |
| Total | $12,496.00 |
How to Use This Calculator
- Enter Deck Length and Deck Width (ft).
- Enter the Decking Cost per sq ft for your chosen material.
- Enter Railing Length (ft) and Railing Cost per ft if railing is part of the project.
- Select Calculate to see the total estimated cost, broken down between decking and railing.
Related Calculations
Planning a fenced-in yard alongside the deck? Estimate materials with the Fence Cost Calculator, or roll the whole project into a broader budget with the Remodeling Cost Calculator.