# Weight on Other Planets Calculator

> Converts a mass (the scale reading on Earth) into the weight in newtons and the equivalent scale reading on Mercury, Venus, Earth, the Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and the Sun, using surface gravity values from the NASA planetary fact sheets.

- Calculator id: `planet-weight` · Category: Biology, Earth & Space (`science`) · Tool name: `calculate_weight_on_planets`
- Canonical page: https://tttkmbb.com/science/planet-weight · This document: https://tttkmbb.com/science/planet-weight.md · JSON definition: https://tttkmbb.com/science/planet-weight.json

## Purpose

Converts a mass (the scale reading on Earth) into the weight in newtons and the equivalent scale reading on Mercury, Venus, Earth, the Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and the Sun, using surface gravity values from the NASA planetary fact sheets.

**Use when:** You want to know how much a person or object would weigh on another planet, the Moon or the Sun, or the gravity ratio between a body and Earth.

**Do not use when:** You need the gravitational force between two arbitrary masses (use gravitational-force) or the weight at altitude or in orbit (use escape-velocity for orbital speeds).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `mass_kg` | number | kg | required | Mass in kilograms, i.e. what a bathroom scale reads on Earth. (> 0, max 1000000000) |
| `body` | enum: mercury \| venus \| earth \| moon \| mars \| jupiter \| saturn \| uranus \| neptune \| pluto \| sun |  | optional, default "mars" | Body for the headline result; the table lists all eleven bodies. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `body_name` | string |  | Selected body. |
| `body_gravity_m_s2` | number | m/s² | Surface gravity of the selected body (NASA fact sheet). |
| `weight_on_body_n` | number | N | mass_kg × g_body. |
| `equivalent_mass_feel_kg` | number | kg | What an Earth-calibrated scale would read: mass_kg × g_body / 9.80. |
| `gravity_ratio` | number |  | g_body / 9.80. |
| `weight_on_earth_n` | number | N | mass_kg × 9.80. |
| `table` | object |  | Equivalent scale reading in kg on each of the eleven bodies, keyed by body. |

## Formula

`weight_N = mass_kg × g_body; equivalent_kg = mass_kg × g_body / 9.80; gravity_ratio = g_body / 9.80`

Surface gravity in m/s² from the NASA planetary fact sheets (values without the centrifugal effect of rotation): Mercury 3.7, Venus 8.87, Earth 9.80, Moon 1.62, Mars 3.71, Jupiter 24.79, Saturn 10.44, Uranus 8.87, Neptune 11.15, Pluto 0.62, Sun 274. Gas giants and the Sun have no solid surface; their value refers to the 1-bar level or the visible photosphere.

## Data Sources

- NASA NSSDCA – Planetary Fact Sheet — https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (government, retrieved 2026-09-24)
- NASA NSSDCA – Sun Fact Sheet — https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html (government, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/planet-weight?mass_kg=…`
- `POST https://tttkmbb.com/api/v1/calculate/planet-weight` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/planet-weight · OpenAPI operationId `calculate_weight_on_planets` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "planet-weight", "inputs": {…}}`

## Example

- 70 kg person on Mars: inputs `{"mass_kg":70,"body":"mars"}` → `{"weight_on_body_n":259.7,"equivalent_mass_feel_kg":26.5,"gravity_ratio":0.3786,"weight_on_earth_n":686,"table":{"jupiter":177.07,"moon":11.57}}`
- 100 kg on the Moon: inputs `{"mass_kg":100,"body":"moon"}` → `{"weight_on_body_n":162,"equivalent_mass_feel_kg":16.53,"gravity_ratio":0.1653}`

```
GET https://tttkmbb.com/api/v1/calculate/planet-weight?mass_kg=70&body=mars
```

## Limitations

You need the gravitational force between two arbitrary masses (use gravitational-force) or the weight at altitude or in orbit (use escape-velocity for orbital speeds). Surface gravity in m/s² from the NASA planetary fact sheets (values without the centrifugal effect of rotation): Mercury 3.7, Venus 8.87, Earth 9.80, Moon 1.62, Mars 3.71, Jupiter 24.79, Saturn 10.44, Uranus 8.87, Neptune 11.15, Pluto 0.62, Sun 274. Gas giants and the Sun have no solid surface; their value refers to the 1-bar level or the visible photosphere. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Does my mass change on other planets?**

No. Mass is the same everywhere; weight (the force of gravity, in newtons) changes with the local gravity, and a scale calibrated on Earth shows mass × g_body / 9.80.

**Why 9.80 and not 9.81 for Earth?**

The NASA fact sheet lists 9.80 m/s²; standard gravity is 9.80665 m/s² and actual values range from about 9.78 at the equator to 9.83 at the poles.

**How can the Sun or Jupiter have a surface gravity?**

It is computed at a reference level: the 1-bar pressure level for the gas giants and the photosphere for the Sun, from GM / R² without rotation.

## Related

- [Gravitational Force Calculator](https://tttkmbb.com/physics/gravitational-force.md) — Newton's law of gravitation for two arbitrary masses.
- [Force Calculator](https://tttkmbb.com/physics/newtons-second-law.md) — Weight as mass × acceleration.
- [Escape Velocity Calculator](https://tttkmbb.com/science/escape-velocity.md) — Escape and orbital speeds of the same bodies.