Geothermal Gradient Calculator
Geothermal Gradient
Calculate subsurface temperature at any depth using the geothermal gradient, surface temperature, and thermal conductivity of rock layers.
Formula
Temperature at Depth = Surface Temp + (Gradient x Depth / 1000); Heat Flow = Gradient x Thermal Conductivity; Depth to 100C = ((100 - Surface Temp) / Gradient) x 1000
Frequently Asked Questions
What is the average geothermal gradient?
The average geothermal gradient is about 25 to 30 degrees Celsius per kilometer of depth. However, it varies widely from 10 C/km in old continental crust to over 80 C/km near volcanic areas and tectonic boundaries.
How deep do you need to drill for geothermal energy?
For electricity generation, wells typically need to reach 150 C or higher, which is usually 2-5 km deep. For direct heating, shallower wells of 1-2 km may suffice. Geothermal heat pumps work at just 3-100 meters.
What is heat flow density?
Heat flow density measures the rate of heat transfer from the Earth interior to the surface per unit area, in milliwatts per square meter. The global average is about 65 mW/m2, higher near plate boundaries and hotspots.
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