Reference Tables
Tables copied from the code and checked cell by cell, with the source and the date it was verified printed on the page. No paraphrased numbers, no "approximately", no rows quietly dropped because they were inconvenient.
A calculator answers one question with your numbers; a table lets you answer the next twenty without coming back. Most of the questions tradespeople actually search for are table-shaped — what size wire for this breaker, what span for this joist, how many conductors fit in this conduit — and the answers people find are usually a manufacturer blog quoting half a table, or a forum post quoting the wrong column of a full one.
These pages exist to fix that specific failure. Each one reproduces the table in full HTML — sortable by eye, readable on a phone, copyable into a job note — states the conditions the numbers are valid under, and names the section and edition it came from. Where a table has footnotes that change the answer, the footnotes are on the page rather than in a PDF nobody opens.
The tables
Wire Ampacity Chart — NEC Table 310.16
Allowable ampacity for 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.
NFPA 70 (NEC) · amperes →Breaker Size Chart — NEC 240.6(A) & 240.4(D)
Standard breaker sizes, 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.
NFPA 70 (NEC) · amperes →Conduit Fill Chart — NEC Chapter 9
How many conductors fit in a raceway: the Table 1 fill percentages, the Table 4 fill area for EMT, IMC, rigid and PVC, and the Table 5 THHN conductor areas, with a working fill look-up.
NFPA 70 (NEC) · square inches →Deck Joist Span Table — IRC 2021 R507.6
The full deck joist span chart — 2×6 to 2×12 by species, 12/16/24″ spacing and all four load cases — with the maximum-cantilever column keyed on back span.
IRC 2021 · feet-inches →Deck Beam Span Chart — IRC 2021 R507.5(1)
Maximum span between posts for 1-, 2- and 3-ply 2×6 to 2×12 deck beams, three species groups at 40 psf live load — entered with the effective joist span.
IRC 2021 · feet-inches →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 and the weight formulas.
ASTM A615 · lb/ft →Roof Pitch Chart — Degrees & Multiplier
Pitch from 1:12 to 12:12 with its angle, slope multiplier and hip and valley factor — and a converter for roof area and rafter length.
Geometry · degrees →Seven tables are live so far. More are being built in the order the questions are actually asked, not alphabetically.
How to read a code table without getting burned
Every table in the IRC and the NEC is a set of answers to one very specific question, and the conditions live in the header, not the title. A table called "Allowable Ampacity" is not a universal statement about a wire; NEC Table 310.16 rates conductors in a raceway, cable or earth with not more than three current-carrying conductors at a 30°C ambient, and every one of those qualifiers can change the answer.
Four habits catch almost every misreading:
- Read the column header before the cell. Most table arguments online are two people reading two different columns of the same table — a 90°C insulation rating against a 60°C termination rating, a 40 psf live load against a 70 psf ground snow load.
- Read the footnotes. The footnotes carry the dead load, the deflection limit (L/360 for main spans, L/180 for cantilevers), the grade of lumber, and the difference between technically permitted and practically sensible. A span table used without its footnotes is not a table lookup, it is a guess.
- Interpolate, never extrapolate. Most of these tables permit linear interpolation between the rows and columns shown, and explicitly forbid extrapolating past them. Beyond the table you are in engineered-design territory, and the honest answer is to say so.
- Check which edition your jurisdiction adopted. The IRC and the NEC are adopted state by state, and amendments are real: several states allow an 8¼″ stair riser where the base IRC says 7¾″. A number is only the code where it was adopted.
How the numbers on this site are checked
Every table page is built the same way. The table is fetched from a primary or near-primary reproduction of the code — the ICC or NFPA text, or a jurisdiction's own published code where the official site is behind a JavaScript reader — and where possible from two independent sources in different jurisdictions, then diffed cell by cell. Anywhere two sources disagree, the page says so and takes the conservative value rather than picking a favourite.
The verification date goes on the page, because code cycles move. It is printed rather than implied so you can judge how stale the page might be before you use it on work that has to pass an inspection.
More tables in progress
Next in the build order:
- Deck beam span chart — the 50/60/70 psf ground-snow tables (R507.5(2)–(4)), once the malformed cells in the published text are resolved.
- The "how far can a 2×10 span" and "how many amps can 12 gauge handle" single-answer lookups, folded into the existing charts.
If you want the table that answers your question today and it is not here yet, the calculator hub already covers the arithmetic behind most of them — concrete volume, rebar and footings, deck framing spans, header sizing, stair geometry, drainage slope, material quantities, room load and conductor sizing.
For the worked reasoning rather than the lookup — the formula shown explicitly, an example you can check by hand, and the mistakes worth avoiding — the guides are the place to start, in particular the 100 amp subpanel wire size guide and the stair math guide.