ForHosting KIT · Developer Utilities

Supplementary angle calculator

A supplementary angle is the angle needed to make a total of 180 degrees. Enter one angle, and this calculator subtracts it from 180 to return its supplement.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

The result is useful when two adjacent angles form a straight line, when a geometry diagram labels a linear pair, or when a triangle problem gives two angles whose sum can first be combined. It also reports the original angle and verifies that both values add to 180 degrees for every calculation.

What a supplementary angle means

Two angles are supplementary when their measures add to exactly 180 degrees. They do not have to touch, but many classroom diagrams show them as adjacent angles on a straight line. That arrangement is called a linear pair: the shared sides form neighboring angles, while the two outer rays point in opposite directions. If one angle measures 65 degrees, its supplement measures 115 degrees because 65 plus 115 equals 180. Supplementary is different from complementary, which describes two angles totaling 90 degrees. It is also different from vertical angles, which are opposite angles created by intersecting lines and have equal measures. This calculator focuses on the supplementary relationship only. Enter the known angle in degrees, and the result gives the missing measure needed to complete the straight-angle total. Values from 0 through 180 are accepted, including decimals, so the tool works for ordinary geometry exercises as well as measurements that are not whole numbers.

How the calculation works

The rule is direct: supplementary angle equals 180 degrees minus the known angle. The calculator applies that subtraction without rounding the input or introducing an approximation. For example, an input of 127.5 degrees produces a supplement of 52.5 degrees. The output also includes a sum of 180 degrees, making the defining relationship easy to check. A known angle must be finite and must lie between 0 and 180 degrees, inclusive. An angle below zero or above 180 cannot serve as one of the two nonnegative parts of a standard supplementary pair, so the calculator rejects it instead of returning a misleading value. Be sure to enter degrees rather than radians. If a problem gives an algebraic expression, such as 3x + 10, solve for the numerical angle first or use the relationship to form an equation. Once the measure is known, enter that number here to confirm the remaining angle.

Using supplements in triangles and linear pairs

In a linear-pair problem, identify the angle whose measure is provided and enter it directly. The returned supplementary angle is the neighboring angle on the straight line. In triangle work, remember that all three interior angles also total 180 degrees. If two triangle angles are known, add them first; the third angle is the supplement of that combined value. For instance, angles of 48 and 72 degrees add to 120 degrees, and the supplement of 120 is 60 degrees, so the third angle is 60 degrees. Exterior-angle diagrams often use the same arithmetic from another direction: an interior angle and its adjacent exterior angle form a linear pair, so either one is the supplement of the other. Always check what the diagram states rather than assuming two angles are supplementary merely because they look adjacent. Geometry drawings may not be to scale. A straight line, a linear-pair label, or an explicit 180-degree relationship provides the justification for using this calculator.

What you can do with it

Complete a linear pair

Find the missing adjacent angle when two angles lie on a straight line and one measure is known.

Find a triangle's third angle

Add the two known interior angles, then calculate the supplement of their total.

Check an interior-exterior pair

Confirm the exterior angle adjacent to a polygon or triangle interior angle.

FAQ

How do I find a supplementary angle?

Subtract the known angle from 180 degrees. The difference is its supplementary angle.

Can supplementary angles have decimal measures?

Yes. Decimal degree measures are valid as long as the known angle is between 0 and 180 degrees.

Are supplementary angles always adjacent?

No. They only need to total 180 degrees. Adjacent supplementary angles whose outer sides form a straight line are a linear pair.

Can I enter radians?

No. This capability accepts degrees. Convert a radian measure to degrees before entering it.

What does the API request cost?

Each API request costs $0.002. The browser calculator is available without an API request.

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

POSThttps://api.kit.forhosting.com/trig/supplementary-angle

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/trig/supplementary-angle \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"angle":65}'

const res = await fetch("https://api.kit.forhosting.com/trig/supplementary-angle", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "angle": 65
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/trig/supplementary-angle",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "angle": 65
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/trig/supplementary-angle", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"angle":65}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"angle":65}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/trig/supplementary-angle", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "angle": 65
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "trig.supplementary_angle",
  "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

Per request$0.002

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.

Read the full KIT documentation →