Radiation Pressure Calculator

Radiation Pressure Calculator

Calculate the pressure exerted by electromagnetic radiation on a surface.

Last updated: March 2026 | By ForgeCalc Engineering

Solar Constant ≈ 1361 W/m²

0 = Black body, 1 = Perfect mirror

Radiation Pressure
9.0796e-6
Pascal (Pa)
Micro-Pascal (µPa)
9.0796 µPa

What is Radiation Pressure?

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. It results from the momentum transfer from photons as they strike or are reflected by a surface.

Although extremely small in everyday life, radiation pressure is significant in astrophysics (e.g., the shape of comet tails) and is the fundamental principle behind solar sails, which use sunlight for spacecraft propulsion.

The Formula

Radiation Pressure Calculation

P = (I / c) × (1 + R)
  • P = Radiation Pressure (Pa)
  • I = Intensity (W/m²)
  • c = Speed of light (≈ 3 × 10⁸ m/s)
  • R = Reflectivity (0 to 1)

Frequently Asked Questions

Why does reflectivity double the pressure?

When a photon is absorbed, it transfers its momentum once. When it is reflected, it must be stopped and then pushed back, transferring twice the momentum.

Is radiation pressure the same as solar wind?

No. Solar wind consists of charged particles (protons/electrons), while radiation pressure is caused by photons (light).

How strong is sunlight pressure on Earth?

It is roughly 4.5 to 9 micro-Pascals. For comparison, atmospheric pressure is about 101,325,000,000 micro-Pascals.

What are solar sails?

They are large, thin, highly reflective sheets that use radiation pressure from the sun to propel spacecraft without carrying any fuel.

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