Documentation sections

PCB Trace Temperature Rise

POSThttps://rftools.io/api/py/v1/calculate

Slug pcb-trace-temp. Calculate PCB copper trace temperature rise under load current with the IPC-2221 external-layer fit and IPC-2152 Figure 5-1. Enter trace width, thickness, and current to get ΔT above ambient. Essential for thermal PCB design and reliability engineering. Free, instant results.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of pcb-trace-temp
Name	Unit	Range	Default	Description
currentnumber	A	at least 0	3	Current
traceWidthnumber	mm	at least 0.1	2	Trace Width
copperWeightnumber	oz	at least 0.5	1	Copper Weight
ambientTempnumber	°C	any	25	Ambient Temperature
traceLengthnumber	mm	at least 1	100	Trace Length
boardThicknessnumber	mm	0.2 … 6	1.6	The whole board’s thickness. Only the board-specific rise (rftools thermal model) reads it; the model is validated from 1.4 to 3.2 mm
planeDistancenumber	mm	0 … 6	0	The dielectric between the trace and the nearest solid copper plane under it; 0 means no plane. Only the board-specific rise reads it
planeCopperWeightnumber	oz	0.5 … 2	0.5	The copper weight of that plane (35 µm per ounce). Only the board-specific rise reads it, and only when there is a plane
isExternalnumber	none	0 … 1	1	It changes only the board-specific rise; the IPC-2221 rise is always chart A, external, and Figure 5-1 is the same on either layerOne of: 1 External (outer) layer · 0 Internal layer
laminatenumber	none	0 … 3	0	The laminate and the board’s total dielectric thickness, which set its maximum operating temperatureOne of: 0 FR-4, ≥ 0.4 mm · 1 FR-4, 0.1–0.4 mm · 2 Polyimide, ≥ 1.6 mm · 3 Polyimide, 0.1–1.6 mm
standardnumber	none	0 … 1	0	The chart the rise is read on: IPC-2221A’s external curve, as Temperature Rise, or IPC-2152’s conservative chart. Either way the limit is the laminate’s maximum operating temperature less the ambient.One of: 0 IPC-2221A Fig. 6-4 · 1 IPC-2152 Fig. 5-1

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of pcb-trace-temp
Field	Unit	Description
tempRiseheadline	°C	Temperature Rise (IPC-2221)
maxTemp	°C	Maximum Trace Temperature (IPC-2221)
traceResistance	mΩ	Trace Resistance
powerDissipated	mW	Power Dissipated
currentCapacity	A	Current Capacity (IPC-2221, ΔT=10°C)
tempRise2152	°C	IPC-2152 Figure 5-1, the conservative chart for internal and external conductors: 4.832 times the IPC-2221 external-layer rise
maxTemp2152	°C	Maximum Trace Temperature (IPC-2152 Fig. 5-1)
inChartRange	none	1 when the Figure 5-1 rise is between 10 and 45 °C and the cross-section at most 700 sq mil, the range the chart draws
tempRiseBoard	°C	rftools thermal model (board-specific): rftools’ own model of a long trace on this FR-4 board in still air, with the plane, if any, under it, and a 15 % margin on the rise. It is not IPC-2152; inside its validated range it is never above the Figure 5-1 rise
maxTempBoard	°C	Maximum Trace Temperature (This Board, Thermal Model)
inModelRange	none	1 when the board-specific rise lies inside the range the thermal model was validated over: Width 0.25–5.1 mm (internal from 1.27 mm), copper ½–3 oz, board 1.4–3.2 mm, a plane from 0.1 mm under the trace to where it fits, plane copper ½–2 oz, rise 5–100 °C, ambient 0–85 °C, the rise before the margin
chartRise	°C	The rise read on the chosen chart: on IPC-2221A’s external curve it is Temperature Rise; on IPC-2152’s conservative chart it is higher
limitRise	°C	The laminate’s maximum operating temperature less the ambient: the most the trace may rise
limitPercent	%	The temperature rise as a percentage of the permissible rise; above 100 % does not comply
minTraceWidth	mm	The width at which the rise equals the permissible rise; at or above it the trace complies
maxCurrent	A	The current at which the rise equals the permissible rise; at or below it the trace complies

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "pcb-trace-temp",
    "inputs": {
      "current": 3,
      "traceWidth": 2,
      "copperWeight": 1,
      "ambientTemp": 25,
      "traceLength": 100,
      "boardThickness": 1.6,
      "planeDistance": 0,
      "planeCopperWeight": 0.5,
      "isExternal": 1,
      "laminate": 0,
      "standard": 0
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("pcb-trace-temp", {
    "current": 3,
    "traceWidth": 2,
    "copperWeight": 1,
    "ambientTemp": 25,
    "traceLength": 100,
    "boardThickness": 1.6,
    "planeDistance": 0,
    "planeCopperWeight": 0.5,
    "isExternal": 1,
    "laminate": 0,
    "standard": 0,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "pcb-trace-temp",
    "inputs": {
      "current": 3,
      "traceWidth": 2,
      "copperWeight": 1,
      "ambientTemp": 25,
      "traceLength": 100,
      "boardThickness": 1.6,
      "planeDistance": 0,
      "planeCopperWeight": 0.5,
      "isExternal": 1,
      "laminate": 0,
      "standard": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "pcb-trace-temp",
	  "inputs": {
	    "current": 3,
	    "traceWidth": 2,
	    "copperWeight": 1,
	    "ambientTemp": 25,
	    "traceLength": 100,
	    "boardThickness": 1.6,
	    "planeDistance": 0,
	    "planeCopperWeight": 0.5,
	    "isExternal": 1,
	    "laminate": 0,
	    "standard": 0
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "pcb-trace-temp",
  "values": {
    "tempRise": 5.342104787621994,
    "maxTemp": 30.342104787621995,
    "traceResistance": 24.63054187192118,
    "powerDissipated": 221.67487684729062,
    "currentCapacity": 3.953008949362809,
    "chartRise": 5.342104787621994,
    "limitRise": 105,
    "limitPercent": 5.0877188453542805,
    "minTraceWidth": 0.3281129167384957,
    "maxCurrent": 11.12374665416563,
    "tempRise2152": 25.814961619314374,
    "maxTemp2152": 50.814961619314374,
    "inChartRange": 1,
    "tempRiseBoard": 10.281805774783722,
    "maxTempBoard": 35.28180577478372,
    "inModelRange": 1
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:pcb-trace-temp",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "IPC-2221A (May 2003) §6.2, Figure 6-4, chart A (the chart of IPC-2221, February 1998), through its published fit; IPC-2152 (August 2009) §5, Figure 5-1; the board-specific rise: rftools thermal model (board-specific), fitted to its own 2-D solver and checked against Brooks & Adam (2015), Jouppi (2010) and Olson (2010)",
    "assumptions": [
      {
        "code": "ipc-2221-external-fit",
        "text": "The IPC-2221 rise is IPC-2221 Figure 6-4 chart A, the external-layer chart, through its published fit with k = 0.048; chart A draws 10 to 100 °C up to 700 sq mil, and the internal-layer chart is not applied to this rise."
      },
      {
        "code": "ipc-2152-figure-5-1",
        "text": "The IPC-2152 rise is read on IPC-2152 Figure 5-1, the chart IPC-2152 recommends for internal and external conductors in all environments, through the same fit with k = 0.024 on either layer; IPC-2152’s corrections for board thickness and a nearby copper plane are not applied."
      },
      {
        "code": "copper-weight",
        "text": "Copper is 35 µm thick per ounce, and the trace cross-section is a rectangle of that thickness."
      },
      {
        "code": "resistance-at-20c",
        "text": "The trace resistance and power use ρ = 1/58 Ω·mm²/m (IEC 60028, 1.7241×10⁻⁸ Ω·m) at 20 °C, not corrected for the trace’s temperature."
      },
      {
        "code": "thermal-model-own-method",
        "text": "The board-specific rise is the rftools thermal model (board-specific): the site's own steady-state model of a long trace on an FR-4 board in still air, with an optional copper plane under it. It is not IPC-2152 and does not read IPC-2152's charts; it is a closed form fitted to a committed 2-D solver, which is checked against published results (Brooks & Adam 2015; Jouppi 2010; Olson 2010)."
      },
      {
        "code": "thermal-model-fr4",
        "text": "The laminate is FR-4, conducting 0.8 W/(m·K) in the plane of the board and 0.3 W/(m·K) through it (Graebner 1995; Azar & Graebner 1996). A laminate that conducts less runs hotter."
      },
      {
        "code": "thermal-model-still-air",
        "text": "The board is horizontal, in still air at sea level. Its faces lose heat by natural convection (the McAdams horizontal-plate correlations, over the 51.2 mm length of the IPC-TM-650 2.5.4.1A test board) and by radiation, with an emissivity of 0.9 for the laminate and 0.1 for the bare copper trace. Forced air, an enclosure and other orientations are not modelled."
      },
      {
        "code": "thermal-model-long-trace",
        "text": "The trace is long and alone. Heat drawn off through pads, vias and leads at its ends, and heat from neighbouring traces and components, are not modelled; a short trace with heat-sunk ends runs cooler."
      },
      {
        "code": "thermal-model-plane",
        "text": "An internal trace lies at the middle of the board's thickness. A plane is one solid copper layer under the trace, across a 76.2 mm (3 in) wide board, the stated distance of dielectric below the trace. A plane above the trace, a second plane, or a plane cut away under the trace is not modelled."
      },
      {
        "code": "thermal-model-margin",
        "text": "The board-specific rise includes a 15 % margin for the model's measured disagreement with published data: it is 1.15 times the model's rise."
      },
      {
        "code": "thermal-model-heat",
        "text": "The model's Joule heat uses the copper resistivity of IPC-TM-650 2.5.4.1A, 10.827 Ω·cmil/ft at 25 °C for 1 oz and heavier copper and 11.529 Ω·cmil/ft for lighter, rising 0.393 % per °C. The resistance and power outputs keep 1/58 Ω·mm²/m."
      },
      {
        "code": "thermal-model-ambient",
        "text": "The board-specific rise is computed at the ambient entered: it sets the air’s properties, the radiation and the copper’s resistivity, so a hotter ambient gives a somewhat larger rise."
      },
      {
        "code": "thermal-model-range",
        "text": "Outside the model's validated range (Width 0.25–5.1 mm (internal from 1.27 mm), copper ½–3 oz, board 1.4–3.2 mm, a plane from 0.1 mm under the trace to where it fits, plane copper ½–2 oz, rise 5–100 °C, ambient 0–85 °C) the board-specific rise is still reported, flagged with a warning naming the bound. On boards thinner than 1.4 mm, IPC-2152's published thickness data show traces running hotter than the model predicts, so the IPC-2152 Figure 5-1 rise is the one to use there."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "current": {
          "min": 0,
          "max": null,
          "unit": "A"
        },
        "traceWidth": {
          "min": 0.1,
          "max": null,
          "unit": "mm"
        },
        "copperWeight": {
          "min": 0.5,
          "max": null,
          "unit": "oz"
        },
        "ambientTemp": {
          "min": null,
          "max": null,
          "unit": "°C"
        },
        "traceLength": {
          "min": 1,
          "max": null,
          "unit": "mm"
        },
        "boardThickness": {
          "min": 0.2,
          "max": 6,
          "unit": "mm"
        },
        "planeDistance": {
          "min": 0,
          "max": 6,
          "unit": "mm"
        },
        "planeCopperWeight": {
          "min": 0.5,
          "max": 2,
          "unit": "oz"
        },
        "isExternal": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "laminate": {
          "min": 0,
          "max": 3,
          "unit": ""
        },
        "standard": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": {
        "description": "IPC-2152 Figure 5-1 through I = 0.024·ΔT^0.44·A^0.725, checked against IPC-2221 (1998) Figure 6-4 chart C (the same chart) at 10 to 45 °C and up to 700 sq mil: the rise is within −5.7 % to +7.3 % of 12 chart readings, and 18 % low at 10 °C and 700 sq mil",
        "worstCaseError": 0.18,
        "inside": true
      },
      "models": [
        {
          "description": "IPC-2152 Figure 5-1 through I = 0.024·ΔT^0.44·A^0.725, checked against IPC-2221 (1998) Figure 6-4 chart C (the same chart) at 10 to 45 °C and up to 700 sq mil: the rise is within −5.7 % to +7.3 % of 12 chart readings, and 18 % low at 10 °C and 700 sq mil",
          "worstCaseError": 0.18,
          "inside": true
        },
        {
          "description": "rftools thermal model (board-specific), a closed-form thermal network fitted to rftools' own committed 2-D solver of the trace's cross-section: Width 0.25–5.1 mm (internal from 1.27 mm), copper ½–3 oz, board 1.4–3.2 mm, a plane from 0.1 mm under the trace to where it fits, plane copper ½–2 oz, rise 5–100 °C, ambient 0–85 °C (the rise before the margin). Inside that range its rise is within 2.81 % of 3,168 solver results",
          "worstCaseError": 0.029,
          "inside": true
        }
      ]
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "current": 3,
      "traceWidth": 2,
      "copperWeight": 1,
      "ambientTemp": 25,
      "traceLength": 100,
      "boardThickness": 1.6,
      "planeDistance": 0,
      "planeCopperWeight": 0.5,
      "isExternal": 1,
      "laminate": 0,
      "standard": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "current"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pagePCB Trace Temperature Rise, at these values