Evaporation Rate Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Thermal calculations often look simple until absolute temperature, sign convention, phase, or heat-transfer mode changes the meaning. Evaporation Rate Calculator keeps the page’s evaporation rate tied to the quantities and assumptions used by this specific thermodynamic relation.

What this calculator does

The Evaporation Rate Calculator brings together Surface area of water, Air speed, Use temperature and RH, Air temperature, Relative humidity around the page’s evaporation rate. The formula section below identifies which values actually drive that result and which fields are supporting or derived quantities, so you can check the page without assuming every visible box is an independent input.

How to use it

The main fields on this page are Surface area of water, Air speed, Use temperature and RH, Air temperature, Relative humidity. Enter the quantities you actually know, keep their units consistent, and leave derived/output-style fields blank unless the formula explicitly allows solving in the opposite direction. For a clean check of evaporation rate, change one driving quantity at a time and confirm that the result moves in the direction predicted by the equation.

How the calculation works

The current estimate multiplies surface area by an empirical air-speed term and a moisture deficit. The deficit can come from the difference between maximum and actual humidity ratio, or from temperature and relative humidity through a saturation-vapor-pressure approximation.

Example

For example, start with the page’s populated scenario: Use temperature and RH = temp_rh. Apply the equation above using the units shown on the page, then compare the calculated evaporation rate with the displayed result. As a second check, change one physical input while holding the others fixed and confirm that the direction of change makes sense for this formula.

How to interpret the result

Interpret evaporation rate within the stated thermodynamic model, unit system, and sign convention. Check whether temperatures are absolute where required and whether the process is idealized, because those details can matter more than the last decimal place.

Limitations and notes

This is an empirical screening estimate rather than a full mass-transfer model. Airflow geometry, vapor removal, surface temperature, activity coefficients, pressure, and natural/forced convection can materially change real evaporation.