Documentation sections

Solder Paste Volume Calculator

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

Slug solder-paste-volume. Calculate solder paste volume, stencil aperture area, and IPC-7525A area ratio. Design SMD stencils for reliable reflow soldering. 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 solder-paste-volume
Name	Unit	Range	Default	Description
padLengthnumber	mm	0.05 … 50	1.5	PCB pad length (in the direction of component lead)
padWidthnumber	mm	0.05 … 50	0.8	PCB pad width
stencilThicknessnumber	mm	0.05 … 1	0.12	Stencil foil thickness (typical: 0.10, 0.12, 0.15 mm)
apertureReductionnumber	%	0 … 50	10	Aperture reduction from pad size per IPC-7525A (typically 10-20%)
releaseCriterionnumber	none	0 … 1	0	The IPC-7525B paste-release rule the stencil is checked againstOne of: 0 Area ratio > 0.66 · 1 Aspect ratio > 1.5

Outputs

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

Outputs of solder-paste-volume
Field	Unit	Description
apertureArea	mm²	Stencil aperture area after reduction
pasteVolumeheadline	mm³	Volume of solder paste deposited per pad
pasteVolumeMl	μL	Volume in microliters (1 mm³ = 1 μL)
areaRatio	none	IPC-7525A area ratio — must be > 0.66 for acceptable paste release
maxStencilThickness	mm	The thickest foil that meets the chosen IPC-7525B rule for this aperture: A/(0.66·P) for the area ratio, W/1.5 for the aspect ratio
stencilPercent	%	The stencil thickness as a percentage of the thickest the rule allows; above 100 % the paste may not release
maxApertureReduction	%	The largest aperture reduction at which the aperture still meets the rule at this foil thickness

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": "solder-paste-volume",
    "inputs": {
      "padLength": 1.5,
      "padWidth": 0.8,
      "stencilThickness": 0.12,
      "apertureReduction": 10,
      "releaseCriterion": 0
    }
  }'

import rftools

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

result = client.calculate("solder-paste-volume", {
    "padLength": 1.5,
    "padWidth": 0.8,
    "stencilThickness": 0.12,
    "apertureReduction": 10,
    "releaseCriterion": 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": "solder-paste-volume",
    "inputs": {
      "padLength": 1.5,
      "padWidth": 0.8,
      "stencilThickness": 0.12,
      "apertureReduction": 10,
      "releaseCriterion": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "solder-paste-volume",
	  "inputs": {
	    "padLength": 1.5,
	    "padWidth": 0.8,
	    "stencilThickness": 0.12,
	    "apertureReduction": 10,
	    "releaseCriterion": 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": "solder-paste-volume",
  "values": {
    "apertureArea": 0.9720000000000002,
    "pasteVolume": 0.11664000000000002,
    "pasteVolumeMl": 0.11664000000000002,
    "areaRatio": 1.9565217391304348,
    "maxStencilThickness": 0.3557312252964427,
    "stencilPercent": 33.733333333333334,
    "maxApertureReduction": 69.64000000000001
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:solder-paste-volume",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "IPC-7525A Stencil Design Guidelines",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "padLength": {
          "min": 0.05,
          "max": 50,
          "unit": "mm"
        },
        "padWidth": {
          "min": 0.05,
          "max": 50,
          "unit": "mm"
        },
        "stencilThickness": {
          "min": 0.05,
          "max": 1,
          "unit": "mm"
        },
        "apertureReduction": {
          "min": 0,
          "max": 50,
          "unit": "%"
        },
        "releaseCriterion": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "padLength": 1.5,
      "padWidth": 0.8,
      "stencilThickness": 0.12,
      "apertureReduction": 10,
      "releaseCriterion": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "padLength"
      ],
      "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 pageSolder Paste Volume Calculator, at these values