Weight calculator
A 70 kg mass under standard Earth gravity of 9.80665 m/s² weighs 686.4655 N. Enter the mass and the local g, such as about 1.62 m/s² for the Moon, to get weight force without confusing mass and weight. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Mass
- 70
- Gravitational acceleration in m/s²
- 9.80665
- Weight
- 686.4655 N
- Precision
- 10
This weight calculator finds the gravitational weight force of an object when you know its mass and the local gravitational acceleration. The definition is the closed form W equals m times g, which is the magnitude of the gravitational force under constant g and matches the first-order model used in introductory mechanics and engineering statics. When mass is given in kilograms and g in metres per second squared, the result is reported in newtons; any consistent unit pair works the same way. Zero mass is valid and yields zero weight; negative mass is rejected because it has no physical meaning in this model. The engine is fully deterministic arithmetic: no network calls, no sampling, and no date-dependent shortcuts.
What weight means and what the result shows
In Newtonian mechanics the weight of a body near a planet or moon is the gravitational force that acts on it, equal to mass times the local gravitational acceleration when g is treated as constant over the region of interest. If m is the mass and g is that acceleration, W equals m times g.
Along a chosen vertical axis the force points toward the attracting body; this calculator returns the signed product so that a positive g with positive mass produces a positive weight magnitude in the usual SI convention, and a negative g (if you supply one for a flipped axis) produces a negative signed force. Apparent weight on a scale can also differ when the support accelerates, but this tool answers the elementary W equals m g form only. Zero mass is valid and yields zero weight when g is finite.
Where weight force fits in study, design, and software
Students meet weight force when a textbook introduces Newton’s second law under gravity, when a statics problem asks for the force a support must carry, or when a contest problem gives mass and a planetary g and asks for W without calculus. Teachers can pre-generate answer keys for modest mass and g values without trusting opaque calculator apps that silently switch units or confuse mass with weight.
Developers call the same contract from scripts to seed deterministic test vectors for game physics demos, to normalize user-entered body mass before a load diagram, or to satisfy programming-challenge statements that demand newtons rather than a hand-waved sketch. Structural and product first-order checks use W equals m g when only mass and a local g are known before safety factors or multi-axis loads are modeled.
What you can do with it
Homework and lab checks
Compute weight force from mass and local g before grading worksheets or comparing to force-sensor data.
Tutoring and teaching software
Normalize user-entered mass and gravity into weight force for interactive lessons and step helpers.
FAQ
What does the weight calculator cost?
It is free in your browser on this page.
What formula is used for weight force?
Weight force is W = m · g, where m is mass and g is gravitational acceleration. With SI inputs (kg and m/s²) the unit is newtons (N).
What happens if mass is negative?
Negative mass is not accepted because weight force W = m·g has no standard meaning for negative mass in this calculator.
Is weight the same as mass?
No. Mass is an intrinsic property of the object. Weight is the gravitational force m·g and depends on the local gravitational acceleration.
Which value of g should I use?
Use the local or problem-stated value. Standard Earth gravity is often taken as 9.80665 m/s²; the Moon is about 1.62 m/s². The calculator does not hard-code a planet.
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/mech/weight-force \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"mass":70,"g":9.80665}'const res = await fetch("https://api.kit.forhosting.com/mech/weight-force", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"mass": 70,
"g": 9.80665
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/mech/weight-force",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"mass": 70,
"g": 9.80665
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/mech/weight-force", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"mass":70,"g":9.80665}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"mass":70,"g":9.80665}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/mech/weight-force", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"mass": 70,
"g": 9.80665
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "mech.weight_force",
"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_mass | 1000000000000000 |
max_abs_g | 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
What weight force means and what the response contains
Weight is not the same as mass: mass is an intrinsic property of the object, while weight depends on the gravitational field and would change on the Moon or in free fall relative to a local frame. The response returns the normalized inputs mass and g, the computed weight, the precision used, a method tag weight_force, a short formula reminder, and a unit hint N for SI inputs. There is no numerical integration of a gravity field and no Monte Carlo sampling of trajectories: the engine either evaluates the product inside the supported numeric range or rejects the input with invalid_input. Rejected cases include a missing mass or g, non-finite values, magnitudes above the documented ceilings, and any mass that is negative, because negative mass is not accepted in this calculator.
How mass and g are read and how W stays reproducible
Zero is allowed and returns zero weight. Use approximately 9.80665 for standard Earth gravity, about 1.62 for the Moon, or a measured local value from a lab; the tool does not hard-code a planet and does not convert unit systems for you. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces and non-numeric tokens are rejected. The preferred field for mass is mass, but aliases m and M are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. Mass must be finite and non-negative: a negative value fails with invalid_input and a message that names the field and explains that W equals m times g is undefined for negative mass in this calculator, so a bad cell does not become a silent nonsense result. The preferred field for gravitational acceleration is g, with aliases gravity, gravity_accel, gravitational_acceleration, and accel_g. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for the numeric outputs, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the weight-force formula yourself.
Where weight force fits in study, design, and software
Product and education tools use the endpoint when a learner types a mass and a gravity value and the UI must show newtons. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with free-fall time or average-acceleration helpers when you need related kinematics, and with other math endpoints when you are building a small lab of free, deterministic physics calculators.
Integration use cases
Deterministic test fixtures
Generate reproducible weight values for unit tests, game-physics demos, and CI assertions on W = m·g.