Nominal pipe size converter
A 2-inch pipe, NPS 2, is DN 50 with an outside diameter of 2.375 in, or 60.3 mm. Look up any of the 34 chart sizes by NPS, DN or measured outside diameter before you order fittings or draw a spool. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 2
- From
- Nps
- From unit
- nps
- Nps
- 2
- Nps label
- 2
- Dn
- 50
A nominal pipe size converter answers the everyday piping question: when a drawing says two-inch pipe or DN fifty, what outside diameter do you actually order in millimetres? Enter a nominal pipe size in NPS inches, a diameter nominal designation, or an outside diameter in inches, millimetres, or centimetres; the tool returns the matching published ASME B36.10M and ISO 6708 row with NPS, DN, OD inches, OD millimetres, and OD centimetres. That mapping is what isometrics, flange catalogs, and mixed SI–imperial BOMs need when a US supplier quotes NPS while a mill sheet lists OD in millimetres.
What NPS, DN, and outside diameter mean
In North American and international process piping, steel pipe is ordered by a nominal designation, not by the free-form diameter you might measure on a solid bar. Diameter nominal, abbreviated DN, is the ISO six thousand seven hundred eight style metric designation that pairs with the same physical pipe: DN fifteen with NPS one half, DN fifty with NPS two, DN one hundred with NPS four, and so on.
Outside diameter is the physical OD of the pipe body used for fittings, insulation clearance, and stress calculations; wall thickness (schedule) changes the inside diameter but does not change the published OD for a given NPS on ASME B thirty-six point ten M carbon steel and related stainless charts. This converter maps a single value among NPS, DN, OD inches, OD millimetres, and OD centimetres against that published table.
It does not encode schedule, wall thickness, internal diameter, pressure rating, material grade, or plastic and copper tube OD systems that use different call sizes. Treat the result as the common steel pipe reference used on process and mechanical drawings, then confirm product sheets when you buy specialty tubing or metric-only product lines.
What you can do with it
Isometrics and flange catalogs
Map stamped NPS or DN call sizes to published outside diameter inches and millimetres before drafting spool drawings and ordering fittings.
Mixed SI and imperial BOMs
Convert millimetre OD readings back to NPS and DN when procuring US steel pipe from a metric shop drawing.
FAQ
What is the outside diameter of 2-inch pipe?
For standard steel pipe, NPS 2 has an outside diameter of 2.375 inches, which is 60.3 mm on the published chart, and pairs with DN 50.
How does NPS relate to DN?
Each published NPS maps to one DN designation on the ASME B36.10M / ISO 6708 style chart—for example NPS 1/2 → DN 15, NPS 2 → DN 50, NPS 4 → DN 100. This tool returns both fields on every success.
Does this include schedule or wall thickness?
No. Schedule changes inside diameter and weight but not the published outside diameter for a given NPS. Use a separate schedule chart for ID and wall.
Is the nominal pipe size converter free?
The browser tool is free and runs locally.
Can I find the NPS from a measured outside diameter?
Yes. Enter the outside diameter in millimetres, inches or centimetres and the converter matches it to the nearest standard row within a tight tolerance, so 60.3 mm comes back as NPS 2 and DN 50.
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/pipe-size \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":2,"from":"nps"}'const res = await fetch("https://api.kit.forhosting.com/conv/pipe-size", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 2,
"from": "nps"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/pipe-size",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 2,
"from": "nps"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/pipe-size", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":2,"from":"nps"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":2,"from":"nps"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/pipe-size", 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": 2,
"from": "nps"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.pipe_size",
"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
Unknown unit names and sizes that are not on the published standard chart are rejected with a clear invalid_input error so automation never invents a phantom bore.
What NPS, DN, and outside diameter mean
Nominal pipe size, abbreviated NPS, is an inch-based call size such as one half, two, or twelve; for NPS one eighth through twelve the outside diameter is larger than the call size, and from NPS fourteen upward the outside diameter in inches equals the NPS number on the standard chart.
How to call the API and what comes back
Absolute magnitudes must stay within the published limit of one million. Send a JSON body with two required fields: value, a finite positive number, and from, a unit string. When from is nps (aliases include nominal, nominal pipe size, and pipe size), value is the NPS in inches—use decimals such as zero point five for one half, one point two five for one and one quarter, or whole numbers for two, four, and six. When from is dn (aliases include diameter nominal and nominal diameter), value is the integer DN designation such as fifteen, twenty-five, or one hundred. When from is od_in, od_mm, or od_cm (with common spellings such as millimetre, outside diameter mm, inch, and centimetre), value is the published outside diameter in that unit and is matched to the nearest standard row within a tight chart tolerance. On success the response echoes rounded value and from, sets nps and nps_label for the inch call, dn for the ISO designation, od_in, od_mm, and od_cm for outside diameter, formula to the table and millimetre factor statement, message to a one-line English summary, steps to an ordered array of substitution lines, supported_units to the five canonical unit ids, and table_sizes to the count of published rows. Failed validation—missing fields, non-finite numbers, non-positive values, sizes absent from the chart, or an unknown unit string—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item.
Practical tips, limits, and related searches
Copper tube, PVC CTS, and metric PE systems use different OD catalogs—do not assume an NPS two result applies to those materials. This landing targets people searching for a nominal pipe size converter, NPS to DN chart, outside diameter millimetres for two-inch pipe, or DN to NPS online; it is not a pressure-drop calculator, not a schedule wall-thickness table, and not a flange face-to-face catalog. Keep values on published standard sizes so results stay on the everyday process and mechanical stock range this page advertises. Prefer sending from as one of the five canonical tokens nps, dn, od_in, od_mm, or od_cm when you control the client; free-form aliases exist for human forms but automation should stay on the short ids. Round-trip checks are easy: convert NPS two from nps, read od_mm of sixty point three, then call again with that millimetre value and from equal to od_mm and confirm nps returns two and dn returns fifty. Remember that NPS is not the same as inside diameter: a two-inch schedule forty pipe has an ID near two inches but an OD of two point three seven five inches, which is what this tool reports. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you deliberately probe unknown units or non-standard sizes.
Integration use cases
Unit tests for piping converters
Generate known-good NPS 2 / DN 50 / OD 60.3 mm fixtures plus deliberate unknown-unit and non-standard-size rejections for commerce tools.
Technical questions
What units are supported?
Canonical units are nps, dn, od_in, od_mm, and od_cm. Common aliases such as nominal, diameter nominal, millimetre, inch, and centimetre are accepted. Unknown names return invalid_input.