AmpSizer is a wire sizing calculator for electricians, apprentices and anyone planning a circuit who needs to know what size conductor it wants. It does the table lookup and the arithmetic around it, and shows which table each figure came from.
One edition, one dataset
The ampacity, temperature-correction, bundling, conduit-fill and conductor-property figures sit in a single generated file that records its edition as the 2023 NEC (NFPA 70, 2023), with each block tagged by its table number, for example Table 310.16 or Chapter 9, Table 8. All 440 reference pages read from that file and name the table they used. The guides link to those pages instead of restating a number.
The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
AmpSizer publishes NEC figures only. The CEC allowable-ampacity tables in CSA C22.1 are a different dataset with different values, different correction factors, and different conditions of use, and nothing on this site substitutes for them. Metric conductor areas convert exactly; ampacities do not convert at all. For Canadian work, size from CSA C22.1 and your provincial amendments.
Who is behind it
AmpSizer was written by one independent developer, who keeps it running. It has no connection to the NFPA, the CSA, a trade association or a manufacturer. The same developer keeps a handful of other single-subject references, among them SpanRef, ThreadRef, SidewallRef and GaugePass, and each has to justify itself on its own subject.
No electrician signs the 4 guides. They carry the AmpSizer name instead, and the page markup names the AmpSizer organization, not a person, as their author. No electrician's licence or engineering credential is claimed.
What it cannot do
A table lookup is not an electrical design. AmpSizer does not carry every exception and condition the code text attaches to a table, it does not know which edition your jurisdiction adopted or what local amendments apply, and it cannot see terminal ratings, equipment listings or the installation in front of you. Final conductor sizing, overcurrent protection and installation belong to a licensed electrician and the approval of your authority having jurisdiction.
Corrections and contact
If a figure here does not match the table it cites, tell [email protected] which page it was on and which table it claims to follow. The fix goes into the dataset, so every page reading from it is corrected at once.
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