🚧 Decking, Fencing & Siding Calculators
📝 Muhammad Ahmad | 🔄 Last reviewed: August 5, 2026 | 8 tools
Outdoor structures are the category where building code shows up most often in a DIY project — guard heights, baluster gaps, stair geometry, post depth. Getting the quantity right matters less than getting the spacing legal.
These calculators flag the relevant code limits as you work, but local amendments always govern. Confirm with your building department before you buy.
Most used in this category
All decking, fencing and siding tools
- Fence Calculator: Boards, Posts & Lumber
Calculate fence posts, panels, rails, and concrete for any fence length. Supports wood, vinyl, chain link, and aluminum fencing with gate allowances. - Baluster Spacing Calculator
Baluster spacing calculator for deck railings. Find how many balusters and the exact even gap that meets the 4-inch code between posts. - Board & Batten Calculator
Board and batten calculator. Find the number of battens, exact on-center spacing, and gap for an evenly spaced accent wall or wainscoting. - Stair Stringer & Rise/Run Calculator
Free stair building calculator: stringer length, rise, run, and tread depth for any total height. Code-compliant calculations for indoor and deck stairs. - How Much Does It Cost to Build a Fence in 2026?
A contractor's cost breakdown for wood, chain-link, vinyl, and aluminum fencing, including a 10-year cost comparison and a printable installation chec - Composite vs. Wood Decking: The 15-Year Cost Breakdown (2026 Guide)
Composite vs Wood Decking: A contractor's 15-year cost breakdown with a cumulative cost crossover chart and a printable wood deck maintenance schedule
Board coverage: why deck material lists always come up short
Decking is sold by the piece in nominal sizes, but it covers in actual sizes, and the gap between the two is where most orders go wrong. A 5/4 × 6 deck board is not 6 inches wide — it is 5½ inches, and once you add the 3/16 in gap that lets it drain and expand, each board only claims about 5.7 inches of deck. Over a 16 ft run that is nearly four extra boards versus the naive calculation.
| Nominal board | Actual width | Coverage with 3/16 in gap | Boards per 100 sq ft |
|---|
| 5/4 × 6 | 5½ in | 5.69 in | ~25 lin ft rows |
| 2 × 6 | 5½ in | 5.69 in | ~25 lin ft rows |
| 2 × 4 | 3½ in | 3.69 in | ~39 lin ft rows |
| Composite 5½ in | 5½ in | 5.69 in | ~25 lin ft rows |
Diagonal decking is the other common miss. Running boards at 45° to the joists looks better and stiffens the frame, but it raises waste from a typical 10% to roughly 15%, because every board takes two angled cuts and the offcuts rarely fit anywhere else.
Post spacing is a code question, not a preference
Fence and railing spacing gets treated as a design choice until an inspector arrives. The figures that actually govern:
- Baluster gap: a 4 in sphere must not pass through any opening in a guard (IRC R312.1.3). This is the "4-inch rule", and it is why baluster spacing is calculated from the gap outward, not by dividing the run into equal parts.
- Guard height: 36 in minimum for residential decks more than 30 in above grade.
- Fence post spacing: 6 ft or 8 ft on centre for most panel systems — 8 ft uses fewer posts but flexes noticeably more in wind and on sloped ground.
- Post embedment: one third of the above-grade height, or below the local frost line, whichever is deeper. A 6 ft fence post is typically a 2 ft hole minimum.
Concrete per post hole. A 10 in diameter hole 24 in deep needs roughly 1.1 cu ft of concrete, or about two 60 lb bags, once you subtract the volume the post itself occupies. For a 100 ft fence at 8 ft spacing that is 14 posts and around 28 bags — a figure worth confirming before you load the truck.
Siding: squares, boxes, and the openings you can actually deduct
Siding is ordered in squares — 100 sq ft of finished coverage. Vinyl typically ships two squares to a box; fibre cement ships by the piece. The deduction rule catches people out: most estimators only subtract openings larger than about 30 sq ft, and deliberately do not deduct standard windows and doors. That is not an oversight. The offcuts around a normal window are largely unusable, so leaving those openings in the gross area is how the waste allowance gets funded.
Add 10% waste on straightforward rectangular walls, and 15% where you have gables, dormers, or a lot of trim intersections. Lap siding on a gable end generates a angled offcut on every course.
Wood, composite, and the point where the money changes hands
Composite decking costs roughly two to three times pressure-treated pine per square foot installed, and the case for it is never the purchase price — it is the fifteen-year total. Pressure-treated needs cleaning and re-sealing every two to three years; composite needs washing. Depending on your labour rate and how diligent you actually are about maintenance, the crossover typically lands somewhere between year eight and year twelve. Our composite vs. wood decking guide lays out the full line-item comparison so you can substitute your own numbers.
Before you order
- Measure twice, at the building. Plans and reality diverge. A wall drawn at 30 ft is often 30 ft 1 in once framed.
- Add a waste factor. Every calculator here exposes one. The defaults are industry-standard ranges, not guarantees — complex layouts need more.
- Confirm code locally. We cite the model IRC where a limit applies. Your jurisdiction amends it, and your building department has the final word.
- These are estimates, not quotes. Useful for budgeting and comparing options; not a substitute for a supplier quote or a licensed professional.
How we derive every figure is set out on our methodology page, including the code sections and manufacturer specs behind each constant.
Other categories