Heat Flux Density Converter

Heat flux (q), or heat flux density, is the rate of heat flowing through each unit of area: watts per square meter (W/m²). It is used for insulation and heat-exchanger design, solar energy, and fire safety.

For a sense of scale: sunlight at the ground is up to about 1,000 W/m², heat through a well-insulated wall a few W/m², and the heat that ignites wood about 12–20 kW/m².

Heat flux follows from a heat transfer coefficient and a temperature difference, q = U * ΔT: a window of 1.4 W/(m²·K) with 20 K across it loses 28 W/m².

How to convert heat flux units

Type a value into any field, and every other unit is calculated at once. For example, 150 kW/m²:

1. In W/m²: multiply by 1,000.

   150 * 1,000 = 150,000 W/m²

2. In Btu/(h·ft²): multiply the W/m² by 0.316998.

   150,000 * 0.316998 = 47,550 Btu/(h·ft²)

Common conversions

The Btu and calorie values are the International Table (IT) units.

Heat flux units

• Watt / meter² (W/m²): One Watt per Square Meter is the SI unit of heat flux and represents one watt of power transferred through an area of one square meter.
  Conversion Factor: 1 W/m² = 1 W/m² (Base Unit)

• Kilowatt / meter² (kW/m²): One kilowatt of power transferred through one square meter.
  Conversion Factor: 1 kW/m² = 1,000 W/m²

• Watt / centimeter² (W/cm²): One watt of power transferred through one square centimeter.
  Conversion Factor: 1 W/cm² = 10,000 W/m²

• Watt / inch² (W/in²): One watt of power transferred through one square inch.
  Conversion Factor: 1 W/in² = 1,550.0031 W/m²

• Joule / second / meter² (J/s/m²): One joule of energy transferred per second through one square meter. Because one Watt (W) is equal to one Joule per Second (J/s), this unit corresponds to one watt per square meter.
  Conversion Factor: 1 J/s/m² = 1 W/m²

• Kilocalorie (IT) / hour / meter² (kcal/h/m²): One kilocalorie of energy transferred per hour through one square meter.
  Conversion Factor: 1 kcal/h/m² = 1.163 W/m²

• Kilocalorie (IT) / hour / foot² (kcal/h/ft²): One kilocalorie of energy transferred per hour through one square foot.
  Conversion Factor: 1 kcal/h/ft² = 12.5184 W/m²

• Dyne / hour / centimeter (dyn/h/cm): One dyne of force applied per hour through one centimeter.
  Conversion Factor: 1 dyn/h/cm = 0.0000002778 W/m²

• Erg / hour / millimeter² (erg/h/mm²): One erg of energy transferred per hour through one square millimeter.
  Conversion Factor: 1 erg/h/mm² = 0.0000277778 W/m²

• Foot pound / minute / foot² (ft•lb/min/ft²): One foot-pound of energy transferred per minute through one square foot.
  Conversion Factor: 1 ft•lb/min/ft² = 0.24323 W/m²

• Horsepower / foot² (hp/ft²): One horsepower transferred through one square foot.
  Conversion Factor: 1 hp/ft² = 8,026.65 W/m²; 1 hp(metric)/ft² = 7,916.84 W/m²

• Btu / second / foot² (Btu/s/ft²): One British Thermal Unit of energy transferred per second through one square foot.
  Conversion Factor: 1 Btu(IT)/s/ft² = 11,356.5 W/m²; 1 Btu(th)/s/ft² = 11,348.9 W/m²

• Btu / minute / foot² (Btu/min/ft²): One British Thermal Unit of energy transferred per minute through one square foot.
  Conversion Factor: 1 Btu(IT)/min/ft² = 189.2754 W/m²; 1 Btu(th)/min/ft² = 189.1489 W/m²

• Btu / hour / foot² (Btu/h/ft²): One British Thermal Unit of energy transferred per hour through one square foot.
  Conversion Factor: 1 Btu(IT)/h/ft² = 3.1546 W/m²; 1 Btu(th)/h/ft² = 3.1525 W/m²

• CHU / hour / foot² (CHU/h/ft²): One Centigrade Heat Unit transferred per hour through one square foot.
  Conversion Factor: 1 CHU/h/ft² = 5.6783 W/m²