Free Construction Calculators
Every calculator on the site, 11 in total — grouped by the work you are actually doing. Each one is free, needs no signup, and runs in the browser.
These are not vibes-based estimators. Where a rule exists in a published code, the tool is built on that rule and the page states which one — the IRC 2021 span and footing tables, IPC 2021 drainage slope, the NEC for conductor sizing, or the manufacturer and Energy Star data behind material quantities. Where no code applies, the page says so and shows the industry practice it is using instead.
Every calculator renders a sensible answer before you type anything, so you can see the expected shape of a result and check your own numbers against it. Units are the ones you work in on site — feet and inches, cubic yards, bags, tons.
Concrete & foundations
3 toolsVolume, bags, and the footing and reinforcement rules that go with them.
Concrete Calculator
Cubic feet, cubic yards, 40/60/80-lb bags and cost, with waste allowance built in.
Open →Rebar & Footing Calculator
IRC 2021 footing width and depth by load, soil bearing, and stories, plus rebar count and lap length.
Open →Deck Footing Size
Minimum footing size from IRC Table R507.3.1 by tributary area, soil, and load.
Open →Framing & structure
3 toolsSpan and member sizing straight from the prescriptive tables, so you are not guessing at a lumberyard.
Deck Beam & Joist Span
IRC 2021 maximum joist and beam spans by species, size, spacing, and load.
Open →Header Size Calculator
Built-up wood header sizing for doors and windows from IRC 2021 R602.7(1)/(2)/(3), with jack studs.
Open →Stair Stringer Calculator
Riser height, tread run, and stringer length, code-checked for residential stairs.
Open →Decks & drainage
2 toolsThe surface and the water: decking layout, and getting drainage to flow the right way.
Landscaping & HVAC
2 toolsBulk material quantities and room load sizing.
Electrical
1 toolsConductor sizing for the runs that are long enough to matter, built on the NEC tables.
Reference tables
not calculators — chartsFull code tables reproduced cell by cell, for the lookups you would rather read than calculate — each with its source and verification date on the page.
Wire Ampacity Chart — NEC Table 310.16
Copper and aluminium, 60/75/90°C columns, 14 AWG to 2000 kcmil, plus the 240.4(D) caps and the ambient and bundle derating factors.
Open →Breaker Size Chart — NEC 240.6(A)
Standard device ratings, the 125% continuous-load rule, the 240.4(B) next-size-up conditions, and the breaker and wire for water heaters, dryers, ranges, AC units and mini-splits.
Open →All reference tables
Every code table on the site, with the section number, the conditions it is valid under, and the date it was verified.
Open →How to use these tools
Measure in the units the tool asks for, and enter the real dimensions rather than rounded ones — a half inch of depth across a slab is a surprising amount of concrete. Add waste where the tool offers it; grade variance and spillage are normal, not a mistake. Then read the quick rules beside each calculator, which state the limits the tool is applying.
If you want the reasoning rather than just the number, the guides walk through the underlying math with worked examples — slab volume, deck board gaps, and stair riser and tread rules.
Something look wrong, or want a calculator we do not have yet? Use the contact page — accuracy reports get priority.