Radiation Pressure Calculator
Radiation pressure is the tiny but real force that photons exert when they strike a surface. Enter the intensity of the radiation, the surface area, and whether the surface absorbs or reflects, to find the pressure in pascals and the total force in newtons.
W/m²
m²
Surface type
Force exerted per unit area by electromagnetic radiation
- 1
Pressure factor
1 (perfect absorber) = 1 - 2
Radiation pressure
1 × 1,361 ÷ 299,792,458 = 0.000005Intensity divided by the speed of light gives pressure in pascals.
How does this calculator work?
Radiation pressure equals intensity divided by the speed of light: P = I/c for an absorbing surface, or P = 2I/c for a perfect reflector. Multiply by area to get the force. At solar intensity (1361 W/m²) the pressure is roughly 4.5 µPa — tiny, but measurable and used in solar-sail spacecraft design.
Formula
How this is calculated
Electromagnetic radiation carries momentum even though photons are massless. When a photon is absorbed by a surface it transfers all its momentum p = E/c to that surface; when it is perfectly reflected, the momentum change is doubled to 2E/c. Integrating over a flux of photons gives the radiation pressure P = I/c for a perfect absorber or P = 2I/c for a perfect reflector, where I is the irradiance (power per unit area, W/m²) and c is the speed of light.
The solar constant at Earth's orbit is approximately 1361 W/m², giving a radiation pressure of about 4.6 × 10⁻⁶ Pa — far too small to feel but measurable and important for spacecraft attitude control and for the design of solar sails. Multiplying pressure by area gives the total radiation force in newtons.
This calculator assumes ideal surfaces (100% absorption or 100% reflection) and a uniform, normally-incident beam. Real surfaces have a reflectance between 0 and 1, so the actual pressure lies between the two limits; oblique incidence further reduces the normal component of force. No relativistic corrections are needed at spacecraft speeds.
Frequently asked questions
Because c ≈ 3 × 10⁸ m/s appears in the denominator. Even the full solar flux at Earth (≈ 1361 W/m²) yields only about 4.6 µPa. The effect is negligible in everyday life but measurable and significant for spacecraft trajectory planning and solar sails over long missions.
An absorbed photon transfers momentum p = h/λ once. A reflected photon reverses direction, so the change in momentum is 2p — doubling the impulse delivered to the surface. Real surfaces with reflectance ρ experience P = (1 + ρ)I/c.
The default intensity (1361 W/m²) is the total solar irradiance at 1 AU from the Sun (Earth's mean orbital distance), per NASA measurements. It varies by ±0.1% with the solar cycle.
Also known as
TG we-Calculate Editorial Team. (2026). Radiation Pressure Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/radiation-pressure-calculator
TG we-Calculate Editorial Team. "Radiation Pressure Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/radiation-pressure-calculator.
TG we-Calculate Editorial Team, "Radiation Pressure Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/radiation-pressure-calculator
@misc{wecalculate_radiation_pressure_calculator, title = {Radiation Pressure Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/radiation-pressure-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?