Construction math that's right the first time.
Fast, accurate calculators for concrete, decking, stairs, and more — built for tradespeople and serious DIYers. No "estimate by vibes." Real formulas, real units, real answers.
Calculators
11 free tools · no signupConcrete Calculator
Volume in cubic feet and yards, bags by size, and estimated cost — with waste built in.
Most used →Deck Beam & Joist Span
IRC 2021 table lookups for max joist and beam spans — by species, size, and spacing.
IRC tables →Stair Stringer Calculator
Riser height, tread run, and stringer length — code-checked for residential stairs.
Framing →Deck Board Spacing
Boards needed for your deck surface, with even gaps and waste allowance.
Decking →Gravel & Mulch Calculator
Yards, tons, bags, and cost for gravel, mulch, sand, and topsoil beds.
Landscaping →Header Size Calculator
What size header for a door or window — built-up wood headers from IRC 2021 R602.7(1)/(2)/(3), with jack studs.
IRC tables →More calculators
code-checked toolsReference tables
straight from the codeCharts copied out of the code cell by cell, with the section number and the verification date on the page — the format these questions are actually asked in.
Wire Ampacity Chart — NEC 310.16
Copper and aluminium, 60/75/90°C columns, 14 AWG to 2000 kcmil, with the 240.4(D) caps and the ambient and bundle derating factors.
Electrical →Breaker Size Chart — NEC 240.6(A)
Standard breaker sizes, the 125% continuous-load rule and the 240.4(B) round-up, plus the breaker and wire for water heaters, dryers, ranges and AC units.
Electrical →Conduit Fill Chart — NEC Chapter 9
How many conductors fit in a raceway: the Table 1 percentages, the Table 4 fill area for EMT, IMC, rigid and PVC, and the Table 5 THHN areas.
Electrical →Deck Joist Span Table — IRC R507.6
The full 2×6 to 2×12 deck joist span chart by species, spacing and load case, with the maximum-cantilever column keyed on back span.
Framing →Deck Beam Span Chart — IRC R507.5(1)
Maximum span between posts for 1-, 2- and 3-ply 2×6 to 2×12 deck beams by species, at 40 psf live load, entered with the effective joist span.
Framing →Rebar Size Chart — ASTM A615
Every standard bar, #3 to #18, with nominal diameter, cross-sectional area and weight per foot, plus a bar take-off to pounds and tons.
Concrete →Roof Pitch Chart — Degrees & Multiplier
Pitch 1:12 to 12:12 with angle, slope multiplier and hip and valley factor, plus a roof-area and rafter-length converter.
Roofing →All reference tables — NEC and IRC charts, each with its source and verification date.
Pick your tool
Concrete, framing, stairs, landscaping — whatever you're building.
Enter your numbers
Feet, inches, spacing, waste. The units you actually work in.
Get a code-checked answer
Results from published tables and formulas — with the code rule stated.
From the guides
Plain-language how-tosConcrete Slab Thickness
How thick a slab should be, the volume formula, waste, and bags vs. ready-mix.
Concrete →Deck Board Spacing
Why gaps matter, how much boards move, and how to keep spacing even.
Decking →Concrete Curing Time
Walk-on, drive-on, and full-load timings, plus why cold weather doubles the wait.
Concrete →Mulch & Gravel Depth
How deep mulch and gravel should be, and how much to order for your beds and paths.
Landscaping →Stair Math
IRC riser and tread limits, the variation rule, and a worked example.
Framing →Deck Stairs
How many steps, the landing depth rule, stringer spans, and the footing exception at grade.
Decks →200 Amp Service Wire
2/0 copper or 4/0 aluminium for a service, 3/0 or 250 kcmil for a subpanel, plus the distance table.
Electrical →Every calculator and guide is built from published code tables and manufacturer specs, then checked against known examples before it goes live.