Solve watts and exposure relationships with clean inputs. Switch units, compare distances, and export results. Built for quick checks across physics, engineering, and fieldwork.
| Source Power (W) | Distance (m) | Surface Area (m²) | Intensity (W/m²) |
|---|---|---|---|
| 100 | 1 | 12.5664 | 7.9577 |
| 100 | 2 | 50.2655 | 1.9894 |
| 250 | 3 | 113.0973 | 2.2105 |
| 500 | 5 | 314.1593 | 1.5915 |
| 1000 | 10 | 1256.6371 | 0.7958 |
Inverse square law for intensity: I = P / (4πr²)
Power from intensity: P = I × 4πr²
Distance from power and intensity: r = √(P / (4πI))
Distance comparison: I₂ / I₁ = r₁² / r₂²
Where:
An inverse square law watts calculator helps you estimate how source power spreads through space. It is useful when radiation leaves a point source evenly. As distance increases, power density falls quickly. The drop follows the square of distance. Double the distance and intensity becomes one fourth. Triple the distance and intensity becomes one ninth. This calculator solves for watts, intensity, distance, and distance comparison values. It supports practical units for field work. It also helps with classroom problems, lighting checks, audio coverage estimates, and simple radiation studies.
Watts describe total source power. Intensity describes how that power spreads over area. The inverse square law connects both values through distance. A larger spherical area means lower power density. That is why a detector receives less energy farther away. This idea appears in optics, acoustics, and nuclear safety. It also appears in antenna studies and lamp placement. When you know any two main quantities, this tool estimates the third. That speeds up early design checks and supports fast technical decisions.
Physics students use this calculator for homework and lab preparation. Engineers use it for source placement and exposure estimates. Safety teams use it for rough radiation screening. Audio teams use it for simple loudness falloff planning. Lighting designers use it to estimate illumination changes with distance. The tool is also useful for sensor planning. It can support camera flash studies and thermal source checks. The example table helps you compare typical values. The export options also make reporting easier during reviews or site visits.
This calculator assumes an isotropic point source. Real sources may beam, reflect, or absorb energy. Walls, air, lenses, and shields can change the result. Large sources also break the pure point source assumption. Near field behavior may differ from simple far field estimates. Use this calculator for baseline analysis, not final certification. Always confirm results with measured data when safety matters. Even with those limits, the inverse square law remains a strong first model. It is fast, clear, and widely used across physics and engineering.
It means intensity decreases with the square of distance. When distance doubles, intensity drops to one fourth. When distance triples, intensity drops to one ninth.
The main internal unit is watts per square meter. You can also enter or review values as milliwatts per square centimeter or watts per square centimeter.
Yes. Choose the power mode. Enter target intensity and distance. The tool returns the source power needed for that exposure level.
It works as a first approximation for any point source that spreads uniformly. Real sound and light systems may need absorption, directionality, and reflection corrections.
That term is the surface area of a sphere. An isotropic source spreads power across that area at distance r. Larger area means lower intensity.
Yes. Use comparison mode. Enter the same source power and two distances. The calculator shows intensity at both points and the ratio between them.
It is useful for screening and planning. For regulated or safety critical work, verify the result with measured data, source specifications, and formal standards.
Beam shaping, shielding, reflections, absorption, and non point sources can change exposure. Near field conditions can also differ from the simple inverse square estimate.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.