Wire ampacity calculator
Copper wire of 12 AWG with 75 °C insulation is rated for 25 amps. Pick the gauge, the temperature class and copper or aluminum to read the reference table value before planning a kitchen, garage or subpanel circuit. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Gauge
- 12
- Temp rating
- 75
- Temp rating c
- 75 A
- Material
- Copper
- Ampacity a
- 25
- Table
- nec_310_16_copper_style
Wire ampacity is the maximum continuous current a copper or aluminum conductor of a given gauge may carry without exceeding its insulation temperature limit under standardized installation assumptions. Homeowners planning a subpanel, electricians sizing branch circuits, makers building shop equipment, and curriculum tools repeatedly look up the same ampacity columns for sixty, seventy-five, and ninety degree Celsius insulation classes—values that map familiar type letters such as TW, THW, and THHN to safe ampere limits for twelve, ten, eight, and larger gauges. Unknown gauges and unsupported gauge-temperature pairs fail with a clear invalid input error rather than a guessed current.
Choosing gauge, insulation temperature rating, and conductor material
Wire gauge is the American Wire Gauge size of the conductor you are evaluating. Everyday branch-circuit copper in homes is often fourteen, twelve, or ten AWG; larger feeders and service conductors use eight, six, four, two, one, and the aught sizes one-ought through four-ought. Insulation temperature rating is the conductor insulation thermal class in degrees Celsius: sixty for many older TW-style ratings, seventy-five for common THW and many terminal temperature limits, and ninety for THHN and similar high-temperature insulations.
Only sixty, seventy-five, and ninety are accepted because those are the three columns published in the reference table this product implements. Material defaults to copper, which matches most residential copper NM and THHN jobs; set material to aluminum when you need the aluminum ampacity column set rather than copper-clad marketing shorthand. Small copper gauges such as eighteen and sixteen only have a ninety degree listing in this table; asking for sixty or seventy-five on those sizes is invalid input, not a zero-amp guess.
What you can do with it
Home branch-circuit wire selection
Homeowners and designers enter AWG twelve at seventy-five degrees Celsius copper to confirm twenty-five amp ampacity before comparing against expected load current for kitchen or garage circuits.
FAQ
Which temperature ratings are supported?
Only 60, 75, and 90 degrees Celsius insulation classes, matching the three common columns (for example TW, THW, and THHN-style ratings).
Is the wire ampacity calculator free?
The browser tool runs free on your device.
Does this replace the National Electrical Code for permit work?
No. Values are a deterministic NEC Table 310.16-style reference for estimates and education. Always apply the current code edition, corrections, and local authority requirements for construction.
What do TW, THW and THHN mean in this table?
They are insulation types that map to the three temperature columns: TW-style ratings to 60 °C, THW to 75 °C, which is also a common terminal limit, and THHN to 90 °C. Choose the class of the wire you plan to install.
What does the table value leave out?
It assumes no more than three current-carrying conductors in a raceway, cable or earth. Ambient temperature corrections, adjustments for more conductors, continuous-load rules and equipment terminal limits are not recomputed, so apply them before choosing a breaker.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/home/wire-ampacity-lookup \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"gauge":"12","temp_rating":75}'const res = await fetch("https://api.kit.forhosting.com/home/wire-ampacity-lookup", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"gauge": "12",
"temp_rating": 75
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/home/wire-ampacity-lookup",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"gauge": "12",
"temp_rating": 75
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/home/wire-ampacity-lookup", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"gauge":"12","temp_rating":75}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"gauge":"12","temp_rating":75}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/home/wire-ampacity-lookup", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"gauge": "12",
"temp_rating": 75
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "home.wire_ampacity_lookup",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
This wire ampacity calculator performs that lookup deterministically from a JSON body: you send gauge and temperature rating, optionally choose aluminum instead of copper, and receive ampacity in amperes with a stable method label.
Choosing gauge, insulation temperature rating, and conductor material
Send gauge as a JSON string or integer—twelve, ten, or one slash zero—and aliases such as awg and wire_gauge are accepted when documented on the parameter schema.
Reading ampacity results, errors, and what the table assumes
The lookup follows commonly published NEC Table three-ten-point-sixteen style values for not more than three current-carrying conductors in raceway, cable, or earth; it is a design-estimate and education tool, not a substitute for the current code edition or the authority having jurisdiction on a job site. On success the response echoes the normalized gauge key, temp_rating_c as sixty seventy-five or ninety, material as copper or aluminum, ampacity_a as the maximum safe continuous current in whole amperes, unit always A, a table label naming the copper or aluminum column set, and method wire_ampacity_lookup so downstream code can branch without sniffing shapes. Use ampacity_a when sizing breakers relative to conductor ampacity in education demos, home-run estimators, BOM checkers, or homework oracles; remember that real installations also apply ambient correction, more-than-three current-carrying conductor adjustments, continuous-load eighty-percent rules, and equipment terminal temperature limits that this reference lookup does not recompute. Unknown gauge strings—metric square millimetres without AWG, nonsense sizes, or gauges outside the published keys—fail with invalid_input and a message that includes unknown gauge. Missing gauge or temp_rating, non-allowed temperature numbers, and aluminum sizes that do not appear in the aluminum table fail the same way and are not charged.
API usage, pricing, workflows, and practical limits
Call the free in-browser wire ampacity calculator for garage remodels, EV charger planning sketches, classroom drills, and quick design checks without opening a PDF code extract. Keep gauges within the published set eighteen through four-ought for copper and twelve through four-ought for aluminum. Send a JSON body with required gauge and temp_rating, plus optional material when aluminum is needed. Use the prepaid API when a home-energy planner, electrical CAD plugin, e-commerce wire configurator, or training platform needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with a watts-volts-amps calculator when you next convert branch power into expected load current, then compare that load against ampacity_a before choosing a breaker education example for a dryer, range, or heat-pump circuit. This product does not derate for conduit fill, ambient above thirty degrees Celsius, rooftop additives, or continuous-load eighty-percent rules—those factors belong in a full design review with a licensed professional.
Integration use cases
E-commerce and BOM wire pickers
Catalog UIs call the API with gauge, insulation class, and material so product pages show maximum safe continuous current without hard-coding tables in every storefront.
Classroom and exam oracles
Instructors pin golden JSON for copper fourteen AWG at sixty degrees and intentional unknown-gauge errors that must fail with invalid_input.
Technical questions
How do I look up wire ampacity with this calculator?
Send JSON with gauge (for example "12") and temp_rating (60, 75, or 90). The response includes ampacity_a in amperes for copper by default; set material to "aluminum" when needed.
What happens if the gauge is unknown?
The request fails with invalid_input and a message that the gauge is unknown or unsupported for the chosen material. Validation failures are not charged.