Watt per Square Inch [W/in²]

The unit watt per square inch (W/in²) measures heat flux density or power per unit area, representing the amount of energy transferred through 1 square inch of surface every second. One watt equals 1 joule per second, so 1 W/in² corresponds to 1 joule of energy passing through 1 in² every second.

This unit is commonly used in high-intensity applications with small areas, such as:

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  Laser beams or focused light sources

  
  
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  Electronic devices to measure power density on chips

  
  
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  Industrial heating processes with concentrated energy

  
  

Heat flux can be expressed as:

where q is heat flux in W/in², Q is energy in joules, A is area in in², and t is time in seconds.

Conversion to SI units:

While W/m² is the SI standard, W/in² is convenient in U.S. engineering, electronics, and laboratory experiments involving small surface areas, where reporting flux per square inch provides an intuitive measure of concentrated energy.

Calorie (IT) per Second per Square Centimeter [cal(IT)/(s·cm²)]

The unit calorie (IT) per second per square centimeter, written as cal(IT)/(s·cm²), measures heat flux density or power per unit area. It represents the amount of International Table calories (1 cal(IT) = 4.1868 J) transferred through 1 cm² of surface every second.

This unit is often used in laboratory-scale heat transfer experiments, solar energy studies, and radiation measurements, especially when dealing with small surface areas where the calorie is convenient. Applications include:

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  Measuring solar energy intensity on small surfaces

  
  
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  Calorimetry experiments on samples

  
  
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  Laser or focused radiation studies

  
  

The heat flux can be expressed mathematically as:

where q is heat flux in cal(IT)/(s·cm²), Q is energy in calories, A is area in cm², and t is time in seconds.

Conversion to SI units:

While W/m² is the SI standard, cal(IT)/(s·cm²) is convenient for small-area, high-intensity heat measurements in laboratory or historical contexts.