Evaporation Calculator
Calculate water evaporation rates for pools, ponds, reservoirs, and open containers. Essential for hydrology, agriculture, pool maintenance, and environmental science.
Interactive Calculator Coming Soon
Use the reference tables and formulas below while the full interactive tool is being built.
What Is Evaporation?
Evaporation is the process by which liquid water converts to water vapour and enters the atmosphere. It is driven primarily by solar radiation, air temperature, relative humidity, and wind speed. Understanding evaporation rates is critical for water resource management, irrigation planning, pool maintenance, and climate science.
Key Factors Affecting Evaporation Rate
- →Temperature: Higher air and water temperature increases molecular energy, accelerating evaporation.
- →Relative Humidity: Low humidity means the air can absorb more moisture, increasing evaporation rate.
- →Wind Speed: Wind removes saturated air above the water surface, continuously exposing it to drier air.
- →Surface Area: Larger water surface = more evaporation in absolute terms (litres/day).
- →Solar Radiation: Direct sunlight adds energy to the water surface, boosting evaporation significantly.
- →Water Salinity: Saltwater evaporates slightly slower than freshwater due to dissolved solutes.
Average Pool Evaporation Rates by Climate
| Climate | Daily Loss (mm) | Monthly Loss (mm) |
|---|---|---|
| Cool & Humid (UK, NW Europe) | 1 – 2 | 30 – 60 |
| Temperate (Central Europe, NE USA) | 2 – 4 | 60 – 120 |
| Mediterranean (Spain, California) | 4 – 6 | 120 – 180 |
| Hot & Dry (Middle East, Arizona) | 6 – 10 | 180 – 300 |
| Tropical (SE Asia, Florida) | 3 – 5 | 90 – 150 |
Frequently Asked Questions
What factors affect evaporation rate?▼
The main factors are temperature (higher = faster), humidity (lower = faster), wind speed (more wind = faster), surface area, and solar radiation intensity.
How much water does a pool lose to evaporation per day?▼
On average, an outdoor pool loses 2–7 mm per day depending on climate. A standard 50 m² pool can lose 100–350 litres daily in warm weather.
How do I reduce pool evaporation?▼
Use a pool cover when the pool is not in use. Covers can reduce evaporation by up to 95%. Windbreaks and lower water temperature also help.