Geothermal Gradient Calculator

About this calculator

The geothermal gradient describes how rock temperature rises with depth beneath the Earth's surface, driven by heat flowing outward from the planet's hot interior. It's typically modeled with a simple linear relationship: T(depth) = surface temperature + (gradient × depth), where the average continental gradient is around 25–30°C per kilometer, though it varies widely near volcanic regions, tectonic plate boundaries, and geothermal fields where gradients can exceed 100°C/km.

Geologists, petroleum engineers, and geothermal energy developers use this calculation to estimate downhole temperatures before drilling — critical for choosing well casing and drilling fluid ratings in oil and gas wells, and for assessing whether a site's subsurface heat is strong enough to justify a geothermal power plant or district heating system.

This calculator takes a surface temperature, a gradient value, and a target depth, and returns the estimated rock temperature at that depth — a fast sanity check that avoids running a full thermal reservoir model just to get a ballpark figure.