Guitar string gauge converter
A 9-gauge high E is 9 thousandths of an inch: 0.009 in, or 0.2286 mm. Turn the gauge printed on a string packet into mils, inches, millimetres, centimetres and micrometres for setup charts, luthier notes and drawings. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 9
- Source unit: gauge
- gauge
- From unit
- gauge
- Gauge
- 9
- Gauge label
- 9-gauge
- Diameter mils
- 9
A guitar string gauge converter turns the number printed on a packet into the core diameter you need for setup charts, CAD notes, and multi-unit BOMs. Enter a musical string gauge (or mils, millimetres, inches, centimetres, or micrometres); the tool returns every common diameter field using the industry identity that gauge number equals thousandths of an inch, then multiplies by exact SI factors—no AWG tables, no guessed tension curves. A nine-gauge high E is nine mils or zero point zero zero nine inches, which is zero point two two eight six millimetres; a forty-two-gauge wound string is forty-two mils.
What musical string gauge means and how diameter is defined
Musical instrument strings—electric and acoustic guitar, bass, mandolin, banjo, and many orchestral specialty packs—are sold by a gauge number that is industry-standard shorthand for the core diameter measured in thousandths of an inch. A packet marked point zero zero nine or nine-gauge is nine mils thick; a forty-six-gauge low E is forty-six mils. That identity is exact by convention and does not depend on alloy, plain versus wound construction, or hex-core versus round-core winding geometry: manufacturers still quote the finished wire diameter in thousandths even when the winding adds mass.
Conversion to SI units is then pure linear factors: one mil equals zero point zero zero one inch, one inch equals exactly twenty-five point four millimetres, one centimetre equals zero point three nine three seven zero zero seven eight seven four inches, and one micrometre is one thousandth of a millimetre. This tool reports gauge, mils, inches, millimetres, centimetres, and micrometres on every success so you can paste the field that matches a setup guide, a luthier worksheet, or a CNC drawing.
It does not compute string tension from scale length and pitch, does not map AWG electrical wire, and does not invent set names such as light or heavy—those marketing labels vary by brand after you know the individual diameters.
Practical tips, limits, and related searches
Keep gauges inside the published inclusive band from one through two hundred mils so results stay within realistic instrument-string diameters and do not collide with electrical AWG or machine-screw charts elsewhere in this catalog. Round-trip checks are easy: nine gauge must yield zero point zero zero nine inches and zero point two two eight six millimetres; feeding that millimetre value back with from equal to mm must recover gauge nine within the published rounding.
When you need electrical AWG diameter and circular mils, use the dedicated wire-gauge converter instead—this landing is musical string core size only. When you need US machine-screw major diameter from a hash number, use the screw-gauge size converter. This page targets people searching for a guitar string gauge converter, string gauge to millimetres, thousandths of an inch to mm, or bass string diameter online; it is not a tension calculator, not a set recommender, and not an AWG tool.
What you can do with it
Luthier setup notes and tech sheets
Convert packet gauge numbers into mm and mils for nut-slot files, saddle compensation charts, and bilingual shop worksheets.
FAQ
What does a guitar string gauge number mean?
By industry convention the gauge number equals the core diameter in thousandths of an inch (mils). A 9-gauge string is 0.009 in thick.
What gauge range is allowed?
Resolved gauge/mils must fall between 1 and 200 inclusive, covering light specialty strings through heavy bass cores.
Is this the same as AWG wire gauge?
No. Musical string gauge is linear thousandths of an inch. American Wire Gauge uses a different logarithmic formula—use the wire-gauge converter for AWG.
Is the guitar string gauge converter free?
The browser tool is free and runs locally.
Can I enter a diameter in millimetres and get the gauge?
Yes. Enter the diameter in millimetres, inches, centimetres, micrometres or mils, and the converter returns the gauge number with every other size. 0.2286 mm, for example, comes back as a 9-gauge string.
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/conv/string-gauge \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":9,"from":"gauge"}'const res = await fetch("https://api.kit.forhosting.com/conv/string-gauge", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 9,
"from": "gauge"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/string-gauge",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 9,
"from": "gauge"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/string-gauge", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":9,"from":"gauge"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":9,"from":"gauge"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/string-gauge", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"value": 9,
"from": "gauge"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.string_gauge",
"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.
Limits
gauge_min | 1 |
gauge_max | 200 |
max_abs | 1000000 |
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
Out-of-range sizes and unknown unit names raise a clear invalid_input error so automation never invents a phantom diameter.
How to call the API and what comes back
Canonical units are gauge, mils, mm, in, cm, and um; common spellings such as ga, thousandths, thou, inch, millimetre, micron, and guitar string gauge normalize to those keys. Absolute value must stay within the published limit of one million, and the resolved gauge in mils must fall between one and two hundred inclusive—enough for light mandolin through heavy five-string bass cores. Send a JSON body with two required fields: value (aliases size, amount, n, gauge, diameter, thickness) as a finite number, and from (aliases from_unit, unit_from, source, unit) naming the source unit. On success the response echoes rounded value and from, sets from_unit to the same canonical key, gauge and diameter_mils to the same mils figure, gauge_label to a short English tag such as nine-gauge, diameter_in, diameter_mm, diameter_cm, and diameter_um for the linear sizes, gauge_min and gauge_max for the published band, formula to the identity and factor string, message to a one-line summary, steps to ordered substitution lines you can assert in tests, and supported_units to the six-key list. Failed validation—missing fields, non-finite numbers, unknown unit names, non-positive diameters, or sizes outside the band—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related searches
Prefer sending numeric value plus a short from key when you control the client; reserve verbose aliases for human forms that accept labels such as thousandths of an inch. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you deliberately probe unknown units or range edges.
Integration use cases
String brand and e-commerce catalogs
Normalize mixed gauge, inch, and millimetre product data into one JSON shape for filters, CAD exports, and comparison tables.
Unit tests for music-gear software
Generate known-good gauge-to-mm fixtures plus deliberate unknown-unit rejections for inventory and setup calculators.
Technical questions
Which units does this converter support?
gauge, mils (thousandths), mm, in, cm, and um (micrometres), plus common aliases. Unknown unit names return invalid_input.