- Select the calculation mode matching your known values.
- Choose a celestial preset or enter custom body data.
- Enter masses, distances, altitude, or field strength.
- Select input and output units before calculating.
- Review the answer, formula, substitutions, table, and graph.
| Example | Known values | Formula | Approximate result |
|---|---|---|---|
| Earth surface | M = 5.97219 × 10²⁴ kg, R = 6371 km | g = GM/R² | 9.82 N/kg |
| Low Earth orbit | Earth data, h = 400 km | g = GM/(R+h)² | 8.69 N/kg |
| Moon surface | M = 7.342 × 10²² kg, R = 1737.4 km | g = GM/R² | 1.62 N/kg |
What gravitational field strength means
Gravitational field strength describes force per unit mass. Its SI unit is newtons per kilogram. It is numerically equal to gravitational acceleration.
A larger source mass creates a stronger field. A larger center distance weakens that field. The change follows an inverse-square relationship.
Distance must start at the center
The point-mass equation uses radial center distance. Surface calculations therefore use the body radius. Altitude calculations add height to that radius.
Using altitude alone gives an incorrect result. The source center remains the geometric reference. This matters greatly near large planets.
Mass, weight, and force
Mass measures the amount of matter present. Weight is the gravitational force acting on mass. The relation is written as F equals mg.
Your mass remains nearly unchanged between planets. Your weight changes with local field strength. This calculator reports both field and force.
Point-mass assumptions
The standard equation treats a source as spherical. It also assumes you are outside its mass distribution. Irregular bodies can require numerical field models.
Rotational effects are not included automatically. Atmospheric buoyancy is also ignored here. Enter a custom constant only for controlled studies.
Multiple sources and vectors
Gravity points toward every attracting source mass. Multiple fields must therefore be added as vectors. Magnitudes alone cannot give the correct direction.
The multi-body mode calculates horizontal and vertical components. Negative coordinates are fully supported. The final angle is measured from positive x.
Is N/kg the same as m/s²?
Yes. The units are dimensionally equivalent for gravitational field strength and acceleration.
Why does gravity decrease with altitude?
Altitude increases center distance. Field strength then falls according to the inverse-square law.
Can the calculator solve for mass?
Yes. Select the source-mass mode and enter field strength plus center distance.
Can it find an altitude?
Yes. Enter body mass, radius, and your required gravitational field strength.
Does test mass affect field strength?
No. Test mass affects gravitational force, but not the source field strength.
What does the vector angle mean?
It gives the net field direction measured counterclockwise from the positive x-axis.
Can I use Earth or solar masses?
Yes. Those units are available for source and multi-body mass inputs.
Are planetary presets exact?
They use representative mean masses and radii. Local gravity can vary slightly.
Does rotation change measured gravity?
Yes. Effective surface gravity can differ because rotation creates centrifugal effects.