LMTD Calculator
Calculate lmtd with transparent engineering inputs and the displayed formula.
Run deterministic checks for missing or mixed units, physical bounds, detectable out-of-range values and formula applicability. This is not an engineering approval or a complete code/compliance check.
Export the current calculation inputs and outputs with formula, assumptions, confirmed source credits, automated verification status, tool version and timestamp.
PROFENG Pro unlocks calculation-record exports. The calculation itself remains free.
PROFENG provides this tool for engineering screening and educational use. Check the calculation basis, units, physical assumptions, applicable standards, safety factors, equipment data and project-specific requirements before design, procurement or operation.
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Why use this lmtd calculator?
Calculate lmtd with transparent engineering inputs and the displayed formula. The displayed relationship is LMTD = (ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂).
What this calculation does
This calculator determines lmtd from terminal temperature difference 1, terminal temperature difference 2. Use it to screen energy, temperature and heat-transfer relationships with explicitly stated properties and boundary conditions.
Formula and engineering variables
LMTD = (ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂)
| Variable | Definition | Unit | Working guidance |
|---|---|---|---|
dt1 | Terminal temperature difference 1 | K | For absolute temperature inputs, values must remain above 0 K. |
dt2 | Terminal temperature difference 2 | K | For absolute temperature inputs, values must remain above 0 K. |
Ranges above are screening guidance or physical bounds where stated. They are not code limits or manufacturer ratings.
Calculated outputs
- LMTD (K): Math.abs(dt1-dt2)<1e-9?dt1:(dt1-dt2)/Math.log(dt1/dt2)
Worked example
- Terminal temperature difference 1 (dt1) = 50 K
- Terminal temperature difference 2 (dt2) = 20 K
Math.abs((50)-(20))<1e-9?(50):((50)-(20))/Math.log((50)/(20)) = 32.741 KLMTD: 32.741 KAssumptions
- Properties entered by the user are treated as constant over the calculation unless the formula explicitly varies them.
- Temperatures and temperature differences must use the unit convention shown by the calculator.
- The model is lumped or one-dimensional where implied by the displayed relationship.
Limitations
- Phase change, radiation, contact resistance, property variation and multidimensional effects can materially change real-system results.
- Use validated property data and the applicable thermal design method for final work.
- Terminal temperature differences must be positive and correspond to one heat-exchanger flow arrangement.
- The LMTD method assumes a steady exchanger and is normally combined with an appropriate overall heat-transfer coefficient and correction factor where required.
- The displayed default values are a worked example only; replace them with traceable project or measurement data.
Formula source and acknowledgement
Relationship used: LMTD = (ΔT1 − ΔT2) / ln(ΔT1/ΔT2), with the equal-terminal-difference limit handled explicitly.
The relationship used here follows Theodore L. Bergman, Adrienne S. Lavine, Frank P. Incropera, David P. DeWitt, Fundamentals of Heat and Mass Transfer 8th edition (2018), Wiley.
Credit for the underlying method belongs to the cited author(s). PROFENG presents its own implementation and wording and is not affiliated with or endorsed by the authors or publishers.
Limits of use for this relationship
- Terminal temperature differences must be positive and correspond to one heat-exchanger flow arrangement.
- The LMTD method assumes a steady exchanger and is normally combined with an appropriate overall heat-transfer coefficient and correction factor where required.
Read the PROFENG methodology for formula sourcing and automated checks →
How to use it
Start with the inputs shown above, review the assumptions or options, then generate the result. Where the tool creates a file, keep the original until you have opened and checked the downloaded output.
Frequently asked questions
What does LMTD Calculator calculate?
This calculator determines lmtd from terminal temperature difference 1, terminal temperature difference 2. Use it to screen energy, temperature and heat-transfer relationships with explicitly stated properties and boundary conditions.
What formula does LMTD Calculator use?
The calculator uses LMTD = (ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂). Every input used by the implementation is listed in the variable table on this page.
How is the worked example for LMTD Calculator checked?
PROFENG substitutes the displayed default values into the implemented relationship and compares the result against automated verification cases where an independent verifier is available.
What assumptions matter most for LMTD Calculator?
Properties entered by the user are treated as constant over the calculation unless the formula explicitly varies them. Temperatures and temperature differences must use the unit convention shown by the calculator. The model is lumped or one-dimensional where implied by the displayed relationship.
Can I use this result for final design or procurement?
Use it as an engineering screening calculation. Final design, procurement, operation or compliance decisions require project-specific data and the applicable engineering method, standard or manufacturer information.
QA, changelog and corrections
Last QA update: 30 September 2026.
Automated verification passed – 30 September 2026 – six numerical cases checked, with dimensional checks, independent cross-checks for calculators, and unit round-trip checks for converters where applicable.
Changelog
30 September 2026 – source/indexation status, metadata and correction pathway reviewed. Engineering tools display the automated verification label only when they are inside the passing Part 3 verification scope.