PCB trace current calculator
A 10 mil outer trace in 1 oz copper with a 10 °C rise carries a little under 1 A. Enter width, copper weight and allowed temperature rise to get the IPC-2221 current for outer or inner layers. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Width
- 10
- Thickness
- 1
- Temp rise
- 10
- Layer
- External A
- Thickness mil
- 1.378
- Area mil2
- 13.78
- K
- 0.048
Printed-circuit-board traces heat as current flows, and the maximum safe current for a given copper geometry is the current that produces an allowed temperature rise above ambient. Layout engineers, power-integrity teams, and makers repeatedly size USB rails, motor drivers, LED strings, and plane necks from trace width, copper weight, and a temperature-rise budget such as ten or twenty degrees Celsius. This PCB trace current calculator applies the IPC-2221 empirical relationship that maps cross-sectional area in square mils and temperature rise to current in amperes, using the published outer-layer and inner-layer constants.
How IPC-2221 turns width, copper, and temperature rise into current
The IPC-2221 generic formula for conductor current-carrying capacity is I equals k times temperature rise to the power 0.44 times cross-sectional area to the power 0.725, with I in amperes, temperature rise in degrees Celsius, and area in square mils. Area is simply trace width in mils multiplied by finished copper thickness in mils.
Copper on fabricated boards is almost always specified as ounces per square foot: one ounce is 1.378 mils, or about thirty-five micrometres, so a ten-mil trace in one-ounce copper has 13.78 square mils of copper in cross-section. The constant k is 0.048 for external (outer) conductors that can convect and radiate from the board surface, and 0.024 for internal conductors buried between dielectric layers, which can carry roughly half the current for the same geometry and rise.
A typical ten-mil, one-ounce, ten-degree outer trace therefore lands a little under one ampere; doubling width or copper weight raises area and current less than linearly because of the 0.725 exponent. For high-current or tightly packed boards you should still review IPC-2152, copper roughness, nearby planes, and manufacturer stack-up notes before freezing a power net.
What you can do with it
Copper-weight trade studies
Compare 1 oz versus 2 oz foil at the same width and temperature rise so fab notes can justify heavier copper on high-current layers.
FAQ
What happens if the trace width is not positive?
Trace width must be greater than zero; a zero or negative width cannot define a copper cross-section. Invalid input is not billed.
Why is internal-layer current lower than external?
Buried traces shed heat less effectively, so the same geometry is rated at about half the current.
How do I convert copper ounces to thickness?
One ounce per square foot is 1.378 mils, or about 35 µm. Multiply that thickness by the trace width to get the cross-section, so a 10 mil trace in 1 oz copper has 13.78 square mils.
Does doubling the trace width double the current?
No. Doubling the width or the copper weight doubles the cross-section, but current grows less than linearly because the area is raised to the power 0.725 in the IPC-2221 relationship.
Is IPC-2221 enough for a high-current board?
Use it as a design estimate. For high-current or tightly packed boards, also review IPC-2152, copper roughness, nearby planes and the manufacturer's stack-up notes, and allow for via necks and solder mask, which are not derated here.
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/elec/pcb-trace-current \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"width":10,"thickness":1,"temp_rise":10}'const res = await fetch("https://api.kit.forhosting.com/elec/pcb-trace-current", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"width": 10,
"thickness": 1,
"temp_rise": 10
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/pcb-trace-current",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"width": 10,
"thickness": 1,
"temp_rise": 10
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/pcb-trace-current", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"width":10,"thickness":1,"temp_rise":10}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"width":10,"thickness":1,"temp_rise":10}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/pcb-trace-current", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"width": 10,
"thickness": 1,
"temp_rise": 10
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.pcb_trace_current",
"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
Send width in mils, copper thickness in ounces per square foot, and allowed temperature rise in degrees Celsius, optionally choosing an internal layer; the response returns current in amperes with the area and constant used. Non-positive trace width is rejected as invalid_input rather than a guessed ampacity.
How IPC-2221 turns width, copper, and temperature rise into current
This endpoint implements that curve fit exactly, with no interpolation tables and no hidden derating for via necks or solder mask. It is a design-estimate tool aligned with the IPC-2221 charts used in countless CAD plugins and textbooks. Identical inputs always produce identical JSON because the path is pure arithmetic with no network, no random seed, and no wall clock.
Input contract, response fields, and error rules
Optional layer is a closed set: external (default, k equals 0.048) or internal (k equals 0.024). If trace width is zero or negative the task fails with a message that width must be positive; that is the contract for this calculator and those failures are not billed. Optional output keys are omitted rather than set to null. POST a JSON body with three required finite numbers: width, the trace width in mils and the field that must be strictly positive; thickness, the finished copper weight in ounces per square foot (common values 0.5, 1, and 2); and temp_rise, the allowed temperature rise in degrees Celsius (commonly 10 or 20). Each field may arrive as a JSON number or as a numeric string. Aliases such as trace_width, width_mil, copper_oz, copper_thickness, temperature_rise, and delta_t are accepted so CAD scripts and spreadsheet exports can map existing column names. Missing fields, non-finite values, non-positive thickness, and non-positive temperature rise fail with invalid_input naming the problem. On success the body echoes width, thickness, temp_rise, and layer, returns thickness_mil (ounces converted at 1.378 mils per ounce), area_mil2, the k actually used, current_a as the maximum safe current in amperes rounded for stable automation, unit always A, a formula string restating IPC-2221, and method ipc_2221 so downstream code can branch without sniffing shapes. The endpoint does not convert millimetres, does not apply IPC-2152 charts, and does not simulate nearby copper pours: it only evaluates the IPC-2221 current from the three geometric and thermal numbers you send.
Where a PCB trace current API earns its keep
Hardware teams use a PCB trace current calculator while drafting power nets so a five-volt rail or a battery-charger path is not drawn at six mils when the load is two amperes. Failed validation does not consume balance. Electronics CAD plugins and DRC helpers call a tiny parse API instead of embedding a brittle copy of the IPC-2221 curve, keeping automation deterministic across regions and languages. Purchasing and fab-note generators compare one-ounce versus two-ounce copper at a fixed width and rise, reading current_a as the benefit of the heavier foil before quoting a stack-up. Keep width in mils and copper in ounces for this endpoint, convert millimetres and micrometres once at the edge if your CAD is metric, pin current_a in tests, and you get reproducible IPC-2221 currents for layout reviews, training, and continuous-integration oracles without standing up a thermal finite-element stack of your own.
Integration use cases
Power-net layout checks
Enter trace width, copper ounces, and a 10 °C or 20 °C rise to confirm current_a before committing a USB, motor, or LED power trace.
CAD plugins and lab oracles
Call the API from a layout script or pin golden JSON, including a non-positive width that must fail with invalid_input.
Technical questions
How do I calculate maximum PCB trace current?
Send width in mils, thickness in oz/ft², and temp_rise in °C. The API returns current_a in amperes from the IPC-2221 formula I = k·ΔT^0.44·A^0.725. Optional layer is external (default) or internal.
What units does the PCB trace current calculator use?
Width in mils (thousandths of an inch), copper thickness in ounces per square foot (1 oz = 1.378 mils), and temperature rise in degrees Celsius. Current is returned in amperes.
What does the PCB trace current calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.