Round to the nearest thousandth
3.14159 rounded to the nearest thousandth is 3.142, and 2.3456 becomes 2.346. Enter any number and keep exactly three decimal places, with a leftover 5 pushing the last kept digit up. Free in your browser.
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Worked example
- Value
- 3.14159
- Rounded
- 3.142
- Display
- 3.142
- Thousandths
- 3,142
Place-value lessons, lab notebooks, and reporting pipelines all need the same quiet contract: take a raw figure that may carry four or more decimal places and snap it to the nearest thousandth. A thousandth is one part in a thousand, written as three digits after the decimal point, so 2.3456 becomes 2.346 under the school half-up rule. This nearest-thousandth calculator applies that rule, the one most answer keys still expect, so a leftover digit of five increases the last kept place away from zero. You send one finite number; you receive the cleaned figure, a numeric rounded value, a three-decimal display string, and the integer count of thousandths. Ties such as one point two three four five become one point two three five, and negative one point two three four five becomes negative one point two three five.
How rounding to the nearest thousandth works
A thousandth is one part in a thousand of a unit, so rounding to the nearest thousandth means keeping exactly three digits after the decimal point and deciding what to do with everything beyond that. The first discarded digit lives in the ten-thousandths place. If that digit is four or less, the three kept thousandths stay as they are.
If that digit is five or greater, one thousandth is added to the kept triple, and carry walks through nines so that nine point nine nine nine five becomes ten point zero zero zero. An exact half-thousandth is treated as a signal to increase magnitude: one point two three four five becomes one point two three five, and negative one point two three four five becomes negative one point two three five. That is the school rule, the Java RoundingMode.HALF_UP rule, and the Python decimal ROUND_HALF_UP rule.
It is not banker's rounding, which would send some half-thousandths toward the even last digit. It is also not a naive JavaScript Math.round of the amount times one thousand, which can lose a half-thousandth to binary residue such as one point two three four five times one thousand. This solver writes the number as a plain decimal digit string, including a faithful expansion of scientific notation, then inspects the fourth fractional digit on that string.
The places count is fixed at three, so you never have to remember whether a thousandth is 0.001 or some other scale.
Where nearest-thousandth rounding shows up in real work
Science and engineering notebooks report masses, voltages, and concentrations to three decimal places so a table stays readable without claiming false precision. Classroom and exam settings that ask students to round to the nearest thousandth need a single trusted oracle for half-cases and negative values so answer keys and student calculators do not diverge. Data engineers normalize imported measurement columns to a fixed three-decimal contract before hashing or comparing rows, cutting flaky equality checks caused by long binary tails.
Manufacturing and quality teams snap gauge readings and millimetre dimensions that already live in thousandths of an inch or of a unit to a documented display. Keep the number inside the published limits, pin the display and thousandths fields in tests, and you get a reproducible nearest-thousandth result for homework, spreadsheets, and edge workers without standing up a decimal-arithmetic library of your own.
What you can do with it
Homework and exam keys on thousandths
Check half-thousandth and negative amounts against a deterministic oracle so 1.2345 and −1.2345 never disagree with the school half-up rule for three decimal places.
Published tables at 0.001 precision
Snap masses, voltages, and gauge readings to the nearest thousandth so a printed table and a machine-readable feed share one documented three-decimal number.
FAQ
What does round to the nearest thousandth mean?
It means keep exactly three digits after the decimal point (one thousandth, or 0.001) and apply half-up to the rest. 2.3454 becomes 2.345; 2.3455 becomes 2.346.
Which rounding rule is used when the next digit is 5?
Half-up, also called half away from zero. A first discarded digit of 5 or greater increases magnitude, so 1.2345 becomes 1.235 and −1.2345 becomes −1.235.
Why is there a display string as well as a number?
The display field always has three decimal places; thousandths is the same value as a signed integer of thousandths.
What does the nearest-thousandth calculator cost?
The browser tool is free and runs locally.
Why not just multiply by 1000, round and divide back?
Because computers store many decimals only approximately, and that shortcut can lose a half-thousandth, as with 1.2345. The calculator reads the digits of your number directly, so 1.2345 reliably becomes 1.235.
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/math/round-to-the-nearest-thousandth \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":3.14159}'const res = await fetch("https://api.kit.forhosting.com/math/round-to-the-nearest-thousandth", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 3.14159
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/math/round-to-the-nearest-thousandth",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 3.14159
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/math/round-to-the-nearest-thousandth", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":3.14159}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":3.14159}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/math/round-to-the-nearest-thousandth", 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": 3.14159
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "math.round_to_the_nearest_thousandth",
"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
max_abs | 1000000000000000 |
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
Missing, infinite, or non-numeric input fails with invalid_input and is not billed. A successful API call costs $0.002.
How rounding to the nearest thousandth works
There is no random seed, no wall-clock timestamp, and no network call; identical numbers always produce identical JSON. Missing value, non-numeric text, NaN, and Infinity fail with invalid_input and are not charged.
What you send and what you get back
Typical checks include three point one four one five nine yielding display three point one four two, one point two three four five yielding one point two three five, nine point nine nine nine five yielding ten point zero zero zero, and negative one point two three four five yielding negative one point two three five. Wire the free browser form for a quick preview, then call the identical contract from scripts when you need bulk normalization before storage or display. Send a JSON body with one required field. value is the finite number to snap to the nearest thousandth; aliases n, number, input, x, num, and amount are accepted when wiring forms or scripts. The field may arrive as a JSON number or as a numeric string in ordinary decimal or scientific notation. A missing field, an empty string, a currency symbol, a thousands separator, NaN, or Infinity fails with invalid_input and names the offending field. Absolute magnitudes above one quadrillion are rejected so the decimal expansion stays inside safe double-precision range on the Worker and in the browser. On success the body echoes the cleaned value, reports rounded as the half-up result as a JSON number, sets display to a three-decimal string so trailing zeros survive JSON (two point zero zero zero stays two point zero zero zero), reports thousandths as the signed integer number of thousandths, and sets method to half_up so clients can document the rule without reading source. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where nearest-thousandth rounding shows up in real work
Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance. This landing targets people searching for round to the nearest thousandth, round to three decimal places, or half-up rounding to 0.001. It does not convert a decimal into a percent, does not reduce a value to significant figures, and does not snap a figure to the nearest ten, hundred, thousand, penny, or a chosen number of decimal places: those are different search intents and different tools.
Integration use cases
Lab and sensor column cleanup
Normalize a CSV or API measurement column to three decimal places and integer thousandths before hashing or comparing rows, so long binary tails do not break equality checks.
Technical questions
What must I send?
A finite number in value (aliases n, number, input, x, num, amount). Currency symbols, empty strings, NaN, and Infinity are rejected with invalid_input.