Measure surface energy transfer with reliable unit conversions. Choose known quantities and get flux quickly. Export results to share, review, and document experiments today.
Units are converted internally to J, s, m², and W for consistent results.
For best accuracy, keep units consistent with your experiment setup.
| Mode | Inputs | Energy Flux (W/m²) |
|---|---|---|
| From Power & Area | Power = 1200 W, Area = 2.0 m² | 600 |
| From Energy, Time & Area | Energy = 50 kJ, Time = 100 s, Area = 1.0 m² | 500 |
| From Flux & Area | Flux = 850 W/m², Area = 3.0 m² (Power result) | 850 |
Examples are illustrative and assume uniform distribution over the area.
Energy flux describes how quickly energy crosses a surface. In many physics and engineering problems, it is the most practical way to compare systems of different sizes because it normalizes power by area. The standard unit is watts per square meter (W/m²), meaning joules per second delivered to each square meter.
Designers use energy flux to size heaters, evaluate insulation, and estimate cooling loads. In field work, it helps compare sunlight, radiative sources, and equipment heat output. For reference, clear noon sunlight at Earth’s surface is often near 900–1,050 W/m², while indoor lighting is typically far lower.
High-intensity sources may be expressed in W/cm² because the numbers become easier to read. Since 1 cm² is 10,000 times smaller than 1 m², a value of 0.10 W/cm² equals 1,000 W/m². This calculator displays multiple units together to reduce conversion mistakes during reporting.
When you know power output and the exposed area, the calculator applies q = P / A. Example: a 1,200 W radiant panel distributing energy uniformly across 2.0 m² produces 600 W/m². This is a fast method for preliminary sizing and quick comparisons.
Experiments often provide total energy over an interval. The calculator uses q = E / (t · A) after converting to joules, seconds, and square meters. For instance, 50 kJ delivered over 100 s to 1.0 m² yields 500 W/m². This mode suits pulses, batch heating, and logged data.
The results panel reports energy flux in W/m² plus alternate units. If you use a mode that solves for power or area, those values appear too. This supports “what-if” checks such as determining required area to keep flux below a target threshold for comfort, equipment limits, or safety margins.
For better estimates, measure the effective area actually receiving energy, not the full device footprint. If flux is non-uniform, use an average or subdivide the surface and compute per section. Keep time units consistent with your data logger to avoid hidden scaling errors.
Energy flux supports heat-transfer comparisons, radiative assessments, and performance benchmarking. In complex systems, losses can occur through reflection, convection, or conduction into supports. Treat the computed flux as an idealized surface-average unless you have calibration data or spatial measurements.
Energy flux is a rate through a surface (W/m²). Energy density describes energy stored per volume (J/m³). One is about transfer; the other is about how much energy exists in a region.
Use energy-based mode when you measured total energy over a time interval, such as a pulse or logged experiment. Use power-based mode when the source output is already known as watts.
Area is commonly measured in m², ft², or cm² depending on the context. Conversions can introduce mistakes, so the tool converts internally to m² and reports consistent results.
Multiply by 10,000 because 1 m² equals 10,000 cm². For example, 0.08 W/cm² equals 800 W/m².
Check whether the active area is smaller than you assumed, or whether time units were entered incorrectly. Also verify unit selections, especially cm² versus m² and minutes versus seconds.
Directional flux can be signed in theory, but this calculator focuses on magnitude for practical reporting. If you need direction, treat the sign separately based on your coordinate convention.
In radiometry, irradiance is radiant power per area (W/m²), which is a form of energy flux. This calculator uses a general physics definition that also applies to non-radiative power transfer.
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.