Example preset
After making a selection, click "Apply" to reflect it in the input.
Inputs
In slope input mode, the chart shows a straight line 1000 m deeper from the reference point (z0, T0).
Results
Details
Temperature-depth graph
With the 2-point method, the chart plots both points and the straight line between them.
The table below provides the chart data.
Reverse solve (advanced / educational)
It is for rough estimation. If the assumptions of the input conditions do not match, please reconfirm with actual data.
Target heat flow → required gradient
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Target heat flow → required k
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Target gradient → required T2
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Assumptions & limits
- This is an approximation assuming only one-dimensional, steady state, and conduction.
- Depth z increases downwards (convention with z=0 at the surface).
- The heat flow rate q_up to be displayed is positive for "upwards toward the earth's surface", and the physical representation q_z=-k(dT/dz) is also shown.
- The formula uses Fourier's law q_z=-k(dT/dz) and also displays HFU (1 HFU = 41.84 mW/m²) from q_up(mW/m²) for reference.
- It does not include the effects of convection, groundwater flow, heat source distribution, unsteady state, or layered structure.
- Please do not use it as a basis for determining design/regulatory compliance; in practice, please follow local data and regulations.
How to use geothermal gradient and heat-flow estimates responsibly
Start from the physical question
Use the direct mode when you already know two temperatures and depths or when you know conductivity and gradient and want heat flow. Use the advanced cards only for quick back-calculations in teaching or rough screening.
Keep sign conventions explicit
This page reports upward heat flow q_up for readability while also showing the physical sign form q_z = -k(dT/dz) with depth positive downward. Do not compare outputs with another source until you confirm both are using the same sign convention and the same heat-flow units.
What the estimate ignores
The model assumes one-dimensional steady conductive transport. It does not include groundwater advection, transient forcing, layered media, or distributed heat sources. If any of those dominate your site, treat this as a rough check only.
Common mistakes to avoid
- Mixing m, km, °C/km, and K/m without checking the converted slope unit.
- Treating site measurements with strong convection or hydrothermal flow as if Fourier conduction alone explained them.
- Using the advanced reverse calculators as a design or regulatory basis without local field validation.
See also
Open the related earth-science and engineering calculators when you need adjacent transport, plume, or environmental conversions after the geothermal estimate itself is settled.
Related tools
- Open channel (Manning method) flow velocity/flow calc | CalcBECompare conductive heat estimates with hydraulic transport questions when flow, not just temperature, matters.
- Effective chimney height (simple plume rise) calc tool | CalcBEUse this when the next step is atmospheric plume dispersion rather than subsurface conductive heat transfer.
- Electricity CO₂ emissions calc (kWh→kg-CO₂ conversion) | CalcBETranslate geothermal or energy estimates into emissions context when the question moves from physics to carbon reporting.
- Moment magnitude Mw calc (fault→M0→Mw) | CalcBEOpen this when the earth-science workflow changes from thermal gradients to fault mechanics and seismic scaling.
- Noise calc (dB addition/distance attenuation) | CalcBEUse distance attenuation tools separately when the engineering task is sound propagation rather than conductive heat flow.
FAQ
What is geothermal gradient?
It is a ratio that shows how much the temperature increases with depth. It can be estimated from the temperature difference and depth difference between two points.
What does heat flux mean?
It is how much heat flows per unit area (W/m²). This tool assumes only conduction and approximates by q≈k×(dT/dz).
The sign is difficult to understand
The physical display is q_z=-k dT/dz (z downward positive), and this tool also displays the upward heat flow q_up=k dT/dz for users.
When should I use the reverse calculators on this page?
Use them only for quick educational back-calculation, such as asking what gradient would be needed to support a target heat flow. They are not a substitute for field inversion or layered-earth thermal modelling.
Why does this page differ from another geothermal tool?
Different tools may use opposite heat-flow sign conventions, different depth coordinates, or conductivity assumptions. Align units and sign definitions before comparing the numbers directly.