Documentation sections

Padstack & Annular Ring Calculator

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

Slug padstack-annular-ring. Calculate minimum pad diameter and annular ring per IPC-6012 for through-hole vias and component pads.

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 padstack-annular-ring
Name	Unit	Range	Default	Description
drillDiameternumber	mm	0.1 … 6.35	0.3	Drill Diameter
platingThicknessnumber	µm	18 … 50	25	Plating Thickness
fabricationAllowancenumber	mm	0 … 0.15	0.05	Fabrication Allowance
ipcClassnumber	none	2 … 3	2	IPC ClassOne of: 2 Class 2 · 3 Class 3
boardThicknessnumber	mm	0.2 … 6	1.6	Board Thickness
standardnumber	none	0 … 1	0	IPC-2221B: the design rule a + 2b + c. IPC-6012E: the Class 3 acceptance ring after the fabrication allowanceOne of: 0 IPC-2221B · 1 IPC-6012E
producibilityLevelnumber	none	0 … 2	1	Sets the IPC-2221B Table 9-1 fabrication allowance c: 0.4, 0.25 or 0.2 mmOne of: 0 Level A (general) · 1 Level B (moderate) · 2 Level C (high)
padDiameternumber	mm	0.1 … 10	0.65	The land diameter on your board, checked against the minimum land of the chosen standard

Outputs

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

Outputs of padstack-annular-ring
Field	Unit	Description
finishedHoleDia	mm	Finished Hole Diameter
minPadDiaExtheadline	mm	Drill + 2 × ring + fabrication allowance, a fabricator's rule; not an IPC-2221 land, which adds a producibility allowance by level
minPadDiaInt	mm	Drill + 2 × ring + fabrication allowance, a fabricator's rule
minAnnularExt	mm	Min Annular Ring (External)
minAnnularInt	mm	Min Annular Ring (Internal)
landAreaExt	mm²	Land Area (External)
aspectRatio	:1	Aspect Ratio
maxAspect	:1	IPC-2222 Table 9-4: Level A up to 5:1, Level B 6:1 to 8:1, Level C 9:1 and up; the same at every class
minLandDiameter	mm	The smallest land the chosen standard allows for this hole: a + 2b + c (IPC-2221B), or the Class 3 ring after the fabrication allowance (IPC-6012E)
landPercent	%	The minimum land as a percentage of the pad; above 100 % the pad is too small
maxDrillDiameter	mm	The largest drill for which this pad still meets the chosen standard

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": "padstack-annular-ring",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "fabricationAllowance": 0.05,
      "ipcClass": 2,
      "boardThickness": 1.6,
      "standard": 0,
      "producibilityLevel": 1,
      "padDiameter": 0.65
    }
  }'

import rftools

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

result = client.calculate("padstack-annular-ring", {
    "drillDiameter": 0.3,
    "platingThickness": 25,
    "fabricationAllowance": 0.05,
    "ipcClass": 2,
    "boardThickness": 1.6,
    "standard": 0,
    "producibilityLevel": 1,
    "padDiameter": 0.65,
})
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": "padstack-annular-ring",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "fabricationAllowance": 0.05,
      "ipcClass": 2,
      "boardThickness": 1.6,
      "standard": 0,
      "producibilityLevel": 1,
      "padDiameter": 0.65
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "padstack-annular-ring",
	  "inputs": {
	    "drillDiameter": 0.3,
	    "platingThickness": 25,
	    "fabricationAllowance": 0.05,
	    "ipcClass": 2,
	    "boardThickness": 1.6,
	    "standard": 0,
	    "producibilityLevel": 1,
	    "padDiameter": 0.65
	  }
	}`)
	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": "padstack-annular-ring",
  "values": {
    "finishedHoleDia": 0.25,
    "minPadDiaExt": 0.45,
    "minPadDiaInt": 0.39999999999999997,
    "minAnnularExt": 0.05,
    "minAnnularInt": 0.025,
    "landAreaExt": 0.08835729338221295,
    "landAreaInt": 0.05497787143782136,
    "aspectRatio": 5.333333333333334,
    "maxAspect": 8,
    "minLandDiameter": 0.6,
    "landPercent": 92.3076923076923,
    "maxDrillDiameter": 0.35
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:padstack-annular-ring",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "IPC-6012E, Table 3-9; IPC-2222 (February 1998), Tables 9-4 and 9-6; IPC-2221 (February 1998), §9.1.1 and Table 9-1",
    "assumptions": [
      {
        "code": "ipc-2221b-base-allowance",
        "text": "The IPC-2221B fabrication allowance is the Table 9-1 base value; its additions for copper heavier than 1 oz/ft² and for boards of more than eight layers are not applied."
      },
      {
        "code": "finished-hole-from-drill",
        "text": "The finished hole is the drill diameter less twice the plating thickness, and stands for IPC-2221B's maximum finished hole a."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "drillDiameter": {
          "min": 0.1,
          "max": 6.35,
          "unit": "mm"
        },
        "platingThickness": {
          "min": 18,
          "max": 50,
          "unit": "µm"
        },
        "fabricationAllowance": {
          "min": 0,
          "max": 0.15,
          "unit": "mm"
        },
        "ipcClass": {
          "min": 2,
          "max": 3,
          "unit": ""
        },
        "boardThickness": {
          "min": 0.2,
          "max": 6,
          "unit": "mm"
        },
        "standard": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "producibilityLevel": {
          "min": 0,
          "max": 2,
          "unit": ""
        },
        "padDiameter": {
          "min": 0.1,
          "max": 10,
          "unit": "mm"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "fabricationAllowance": 0.05,
      "ipcClass": 2,
      "boardThickness": 1.6,
      "standard": 0,
      "producibilityLevel": 1,
      "padDiameter": 0.65
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "drillDiameter"
      ],
      "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 pagePadstack & Annular Ring Calculator, at these values