Deck Calculator
Estimate the decking boards, joists and area for a deck from its length and width. Example: a 12 by 16 foot deck with 5.5 inch boards needs about 29 sixteen-foot boards with 10% waste and 13 joists at 16 inch spacing.
Show steps
How to use the Deck Calculator
- Enter the deck length and width.
- Choose the board width and length, gap, joist spacing and waste.
- Press Calculate for boards and joists.
Formula and method
Rows of boards = deck width in inches / (board width + gap). Boards = rows x boards per row x (1 + waste). Joists = deck length in inches / spacing + 1.
Worked example: 12 x 16 ft deck
| Step | Result |
|---|---|
| Rows (144 / 5.625) | 26 |
| Boards of 16 ft per row | 1 |
| With 10% waste | 29 boards |
| Joists (192 / 16 + 1) | 13 |
Deck area and boards for 16 ft boards (5.5 in)
| Deck | Area | Boards (10% waste) |
|---|---|---|
| 8 x 10 ft | 80 sq ft | 20 |
| 10 x 12 ft | 120 sq ft | 25 |
| 12 x 16 ft | 192 sq ft | 29 |
| 14 x 16 ft | 224 sq ft | 33 |
| 16 x 16 ft | 256 sq ft | 39 |
Before you build
Most areas require a permit for decks over a certain height or size. Use pressure-treated lumber for framing, stainless or coated fasteners, and flashing where the deck meets the house.
Frequently asked questions
How many deck boards do I need?
Find the number of rows across the width, multiply by boards per row, and add waste.
How far apart should joists be?
16 inches on center is common; 12 inches for diagonal decking or composites.
How much gap between deck boards?
About 1/8 inch for wood to allow drainage and swelling.
How much waste should I allow?
About 10%, or 15% for diagonal layouts.
Do I need a permit?
Usually, especially for attached or raised decks.
What size are 2×6 boards?
Actually 1.5 by 5.5 inches.
Sources
- American Wood Council: Prescriptive Residential Wood Deck Construction Guide (DCA 6)
- International Residential Code
Related calculators
Related to This Article
More math articles
- Understanding Trigonometry: How to Calculate the Area of Triangles
- Each trade creates surplus when benefit exceeds cost
- Top 10 SAT Math Practice Questions
- How to Graph Transformation on the Coordinate Plane: Reflection?
- Wrenches, Sockets, and Pliers: Making the Right Match
- How to Solve Multi-step Word Problems for Finding Starting and Ending Times
- Citing Text Evidence in Grade 6: How to Move from Vague Answers to Strong Analysis
- Rounding Numbers Up to the Millions
- Specialty, Powered, Endoscopic, and Ophthalmic Instruments
- Tile Calculator
What people say about "Deck Calculator: Decking Boards, Joists & Area"?
No one replied yet.