Read this first. No result on this page is a project estimate. No result from a tool here describes a place, a well or a project. Each tool does arithmetic on the numbers you type, and nothing more. The figures in the tables are what each source says, and each table gives the date the sources were read.
Four sections follow. Each shows its equation or factors and the source for them. Sections 1, 2 and 4 end with a small tool you can run. Everything runs in your browser and nothing is sent.
1. Pressure gradient
USGS defines the nominal pressure gradient as the measured pressure divided by the depth, and gives it in psi per foot. The tool below does that division.
pressure gradient = pressure / depthpressure in psi, depth in ft, result in psi per ft. Use the pressure and the depth for the same point.
The reference points differ by source. The table gives each one as the source states it.
| Source | Normal (hydrostatic) reference | What it says about higher gradients |
|---|---|---|
| USGS Circular 790, 1979 | 0.465 psi per ft, about 10.5 kPa per m | Geopressured rocks have pore fluid pressure above normal. The sentence that defines the term gives no gradient at which geopressure starts. |
| Bureau of Economic Geology, 1982 | 0.465 psi per ft | Picked the "operational" top of geopressure in the Wilcox trend of the Texas Gulf Coast at approximately the depth where the gradient is 0.7 psi per ft. |
| DOE program paper, abstract, 1989 | 0.465 psi per ft | Geopressured reservoirs exceed the normal gradient. The abstract also says pressures have been measured as high as 1.05 psi per ft in the Gulf Coast area. The sentence that gives it names no well or formation, and the figure is a maximum, not a typical value. |
| NREL presentation, 2012 | Not stated in the passage read | A study working definition: a brine reservoir hotter than 212 degrees F with a gradient above 0.7 psi per ft. |
| USGS report on Utah and Colorado drill-stem tests, 2003 | 0.433 psi per ft for fresh water. The report says the gradient varies with salinity, temperature and depth, and gives 0.444 psi per ft for one worked example of water with a density of 1.027 g/cm3 | Used here only for the water-column reference. |
The sources do not use one number, so the tool below does not compare your result with any of them. It divides and prints the arithmetic.
Sources: Subsurface Pressures from Drill-Stem Tests, Uinta and Piceance Basins, USGS, 2003; Circular 790, USGS, 1979; Report of Investigations 117, Bureau of Economic Geology, 1982; Properties of Geopressured Brines and Wells in the Gulf Coast and Opportunities for Industrial/Research Participation, conference paper, Idaho National Engineering and Environmental Laboratory for the U.S. Department of Energy, 1989; Recoverable Resource Estimate, NREL, 2012. Read October 4, 2026.
Divide a pressure by a depth
2. The heat relation
NASA Glenn says the heat transferred between two objects is proportional to the temperature difference and to the heat capacity of the object. It also says a specific quantity is per unit of mass, and that multiplying it by the amount of substance gives the actual value. Put together, heat equals mass times specific heat times temperature change. NASA works this out for a gas at constant pressure and does not itself print the equation below; it is the combination of those two passages. For a fluid that flows, the tool uses the amount per second.
Q = m x cp x delta TQ is heat rate in kW. m is mass flow in kg/s. cp is specific heat in kJ/(kg K). delta T is a temperature difference in K.
The units work out as kg/s times kJ/(kg K) times K, which is kJ/s. One kilowatt hour is 3.6 MJ and one hour is 3,600 s, so one kW is one kJ/s. The tool also shows Q in MWt, which is thermal power in megawatts and is kW divided by 1,000.
| Input | Meaning | Unit |
|---|---|---|
| m | Mass flow of the fluid. A flow given as a volume needs a density to turn it into mass. | kg/s, or L/s, gal/min or bbl/day with a density in kg/m3 |
| cp | Specific heat of the fluid. You supply it from your own source. | kJ/(kg K) |
| delta T | The temperature difference, such as the drop across a heat exchanger. | K, deg C or deg F |
| Q | The result. | kW, also shown as MWt |
A difference of 1 deg C is a difference of 1 K, and a difference of 1 deg F is 5/9 K, so the tool divides a deg F difference by 1.8 to get K. The tool does not refuse a negative temperature difference or a zero flow. It does the arithmetic and prints a negative or zero result.
Two values for water
NIST gives the specific heat of pure liquid water at 25 degrees C and 1 atm as 4.1813 kJ/(kg K). USGS gives 4,184 joules to warm one kilogram of water by 1 degree C. The first is stated for pure water. The USGS page does not say which water. A brine is not pure water, and this page has no source for how its specific heat compares. It makes no statement of how much.
A worked example, with made-up numbers
The numbers are invented for practice. They are not a flow, a temperature drop or an output of any well. Written out by hand:
10 kg/s x 4.18 kJ/(kg K) x 50 K = 2,090 kW = 2.09 MWtMade-up numbers. The button in the tool loads these same numbers.
Sources: Heat Transfer and Specific Heat, NASA Glenn Research Center; NIST Chemistry WebBook, Isobaric Properties for Water; Specific Heat Capacity and Water, USGS Water Science School; NIST Guide to the SI, Appendix B.8 and Special Publication 811, National Institute of Standards and Technology, for the hour, the kilowatt hour and the temperature difference; Kilowatthour, U.S. Energy Information Administration; Circular 790, USGS, 1979, for MWt. Read October 4, 2026.
Calculate a heat rate
3. MWt and MWe are different quantities
EIA defines a megawatt as one million watts of electricity, and megawatt electric (MWe) as one million watts of electric capacity. In Circular 790, USGS used MWe for electrical power and MWt for thermal power in megawatts to avoid confusion.
The heat tool prints MWt, a thermal quantity. This site never converts MWt to MWe, and it gives no efficiency. A thermal figure is not an electric capacity.
Sources: EIA Energy Glossary (M), U.S. Energy Information Administration; Circular 790, USGS, 1979. Read October 4, 2026.
4. Unit conversions
The converter handles pressure (psi, kPa), length (ft, m), temperature (deg F, deg C, K), volume (bbl, US gal, m3) and power (kW, MW, BTU/h, MMBtu/h). It has no energy units: it does not convert kWh, J or Btu. The table gives the NIST and EIA factors and definitions behind it. Its two temperature rows give the interval factors this page cites: a difference of 1 deg C is 1 K, and a difference of 1 deg F is 5/9 K. The converter reads a deg F, deg C or K value as a temperature reading, using the formulas set out after the table. The converter uses the factors as the NIST table prints them: 6.894757 kPa per psi, 0.3048 m per ft, and 0.003785412 m3 per US gal, with a barrel counted as exactly 42 US gal. Btu per hour is covered after the table.
| Conversion | Factor | Source |
|---|---|---|
| Pressure | 1 psi = 6.894 757 kPa | NIST |
| Length | 1 ft = 0.3048 m, exact | NIST |
| US gallon | 1 gal = 0.003 785 412 m3, or 3.785 412 L | NIST |
| Petroleum barrel | 1 bbl, which is 42 US gal, = 0.1589873 m3, or 158.9873 L | NIST |
| Btu to joule | 1 Btu (International Table) = 1,055.056 J. 1 Btu (thermochemical) = 1,054.350 J. The International Table Btu is exactly 1.055 055 852 62 kJ, based on a calorie of 4.1868 J. | NIST |
| Hour | 1 h = 3,600 s, exact | NIST |
| Kilowatt hour to joule | 1 kWh = 3.6 MJ, exact | NIST |
| Temperature difference, deg C | 1 deg C difference = 1 K difference | NIST |
| Temperature difference, deg F | 1 deg F difference = 5/9 K, or 0.5555556 K | NIST |
| Btu | One Btu is the heat needed to raise one pound of water by 1 degree F. | EIA |
| MMBtu | One million Btu. | EIA |
| Kilowatt hour to Btu | 1 kWh is 1 kW for 1 hour, equal to 3,412 Btu. | EIA |
The Btu per hour factors are 0.0002930711 kW per BTU/h and 293.0711 kW per MMBtu/h. They follow from the table: 1,055.056 J per Btu (International Table) divided by 3,600 s is 0.2930711 W, which is 0.0002930711 kW, and an MMBtu is one million Btu. A megawatt is 1,000 kW. A temperature reading is not a temperature difference. A reading in K is the reading in deg C plus 273.15, while a difference is the same number in both. The temperature converter works on readings, and the heat tool works on differences. To turn a deg F reading into deg C, the converter subtracts 32 and divides by 1.8. To turn a deg C reading into deg F, it multiplies by 1.8 and adds 32. To get K it adds 273.15 to the deg C value, and to get deg C from K it subtracts 273.15. These are the formulas the converter uses. The table rows list the interval factors, not these formulas. The converter shows results to at most six decimal places, so a very small result can differ from a factor printed here.
Sources: NIST Guide to the SI, Appendix B.8 and Special Publication 811, National Institute of Standards and Technology; British thermal units (Btu), MMBtu and Kilowatthour, U.S. Energy Information Administration. Read October 4, 2026.