Deck calculator app: boards, framing and cost on your phone (2026)

A deck calculator app should get you from "a 12 by 16 deck off the back door" to a lumber list and a price range you trust, while you're standing in the yard. The difference between a useful one and a toy is whether it counts boards the way a lumber yard sells them, sizes the framing, and shows its assumptions. This guide covers what to look for, a worked example to check any app against, and the free options on Android, iPhone and the web.

Short answer: on Android, our Deck Calculator & Cost Planner is free on Google Play: every calculator is free with ads, and optional one-time purchases add contractor tools or remove ads. On iPhone, the deck calculator is part of Roofing Calculator & Estimator (version 1.7 and later). On a laptop, use the free calculators at smartdeckingcalculator.com.

What a good deck calculator app should do

• Count boards in lengths you can buy. "192 sq ft of decking" is useless at the lumber desk. You want 26 boards at 16 feet, with the offcuts accounted for.
• Handle board direction, gaps and borders. Diagonal boards and a picture-frame border change the count and the waste.
• Size the framing, not just the surface. Joists, beams, posts and footings, checked against a span table (in the US, IRC R507), with a clear note that your local inspector decides.
• Do stairs and railings. Stringer layout, riser and tread sizes, and baluster spacing to the 4-inch sphere rule.
• Give a cost range, not one number. Material and labor vary by region and by material (pressure-treated, cedar, composite, PVC). A range with editable assumptions is more honest.
• Work offline and save projects. And export a list you can hand to a supplier.

Deck Calculator & Cost Planner (Android): what's in it

From the app's Google Play listing (checked October 4, 2026):

• a deck drawn to scale as you type the size, with board courses, joists, stairs and railing posts; offcut-aware board counts;
• a deck cost calculator with low, typical and high figures by material, DIY or contractor, and state;
• cost per square foot, 14 common deck sizes from 8x8 to 20x30, composite vs wood over 25 years, railing and stair costs, and a contractor quote checker;
• joist span checks against the IRC R507.6 tables, beam sizing, post count, footing size and frost depth, stair stringer layout and baluster spacing;
• saved projects shareable as text or PDF, a price book and quotes for contractors;
• 100 tools that run with no signal, no account; every calculator free with ads, with optional one-time Pro and Remove Ads purchases and no subscription.

A worked example you can check by hand

A 12 × 16 ft deck with boards running the 16-foot way, 5.5-inch-wide boards and a 1/8-inch gap:

1. Each board covers 5.5 + 0.125 = 5.625 inches. Across 12 ft (144 in): 144 ÷ 5.625 = 25.6, so 26 boards at 16 ft.
2. Joists run the other way, across the 12 ft, at 16 inches on centre along the 16 ft: 192 ÷ 16 = 12 spaces, so 13 joists at 12 ft (plus rim joists).
3. Add about 10% for bad boards and cuts on a simple rectangle: order 29 boards. Diagonal decking needs closer to 15%.
4. Check the joist size against your local span table before you buy. A 12 ft span at 16 inches on centre is past what 2x6 joists allow under the IRC tables, so expect 2x8 or larger depending on the species.

If an app gives a very different board count for the same deck, check its board width, gap and waste settings. Our deck cost calculator guide walks through pricing the same deck.

On iPhone

Roofing Calculator & Estimator on the App Store includes a deck calculator alongside fence, drywall, insulation, tile, sod and gravel calculators, so one free app covers most outdoor projects. The web calculators at smartdeckingcalculator.com also work well in Safari.

Related projects

Building a fence around the new deck? See the fence calculator app guide. Need a gravel pad or path under it? See gravel calculator apps. Quoting decks for customers? Instant Quote Maker turns the numbers into a PDF quote.