Free concrete tool
Concrete Evaporation Rate Calculator
Estimate the surface evaporation rate of a fresh concrete pour with the ACI 305 equation, so you know when plastic shrinkage cracking is a real risk before the trucks show up.
Concrete Evaporation Rate Calculator
Enter air temperature, concrete temperature, relative humidity, and wind speed to get the ACI 305 surface evaporation rate. Free, no sign-up required.
Surface & Weather Conditions
Range -40 to 140 °F
Always entered or confirmed manually
Range 0 to 100 %
Range 0 to 100 mph
Notice: This calculator estimates evaporative conditions using entered or imported weather data. It is a planning aid and not a direct measurement of actual concrete surface water loss. Verify job-site conditions, project specifications, and applicable industry guidance before placement.
What the evaporation rate calculator does
The concrete evaporation calculator takes four inputs — air temperature, concrete temperature, relative humidity, and wind speed — and returns the rate at which surface moisture leaves fresh concrete. Work in US units (°F, mph, lb/ft²/hr) or metric (°C, km/h, kg/m²/hr); MudHub converts and runs the ACI 305 equation either way.
ACI 305 equation
Deterministic implementation of the standard nomograph formula — the same math, without reading a chart in the truck.
Live weather import
Pull current conditions for the job site and see the nearest recognizable town, station distance, and observation time.
Risk guidance
Results are compared against the 0.2 lb/ft²/hr precaution threshold so the call is obvious on site.
Saved to the project
Store the snapshot with the job. Reopening it preserves the original values and conditions.
What concrete evaporation rate means
Evaporation rate is how fast water leaves the surface of fresh concrete, measured in pounds per square foot per hour. When water leaves faster than bleed water rises to replace it, the surface dries and shrinks while the concrete underneath hasn't moved yet. That is when plastic shrinkage cracks open — before final set, often before finishing is done.
Inputs that affect evaporation
Air temperature
Warmer air holds more moisture, but on its own it is not the whole story.
Concrete temperature
Warm concrete drives evaporation harder. Concrete warmer than the air — common on cool mornings with a hot mix — can push the rate up even on a mild day.
Relative humidity
Dry air pulls moisture off the surface faster. Lower humidity means a higher rate.
Wind speed
Wind sweeps moist air off the surface and replaces it with dry air. It is often the biggest single factor.
Why wind matters
Holding 85°F air and concrete at 30% humidity, the calculator gives about 0.04 lb/ft²/hr with no wind, 0.22 at 10 mph, and 0.40 at 20 mph. The temperature didn't change — the wind did. That's why a breezy, mild day can be riskier than a still, hot one.
Example conditions
| Air | Concrete | Humidity | Wind | lb/ft²/hr | Category |
|---|---|---|---|---|---|
| 70°F | 70°F | 50% | 5 mph | 0.06 | Lower |
| 85°F | 85°F | 30% | 10 mph | 0.22 | High |
| 75°F | 80°F | 40% | 20 mph | 0.33 | High |
| 90°F | 95°F | 25% | 15 mph | 0.46 | High |
Calculated with the MudHub calculator; categories as shown in the tool.
Ways contractors manage high evaporation
- Schedule the pour for cooler, calmer hours.
- Set up windbreaks and sunshades.
- Fog the air above the slab (without puddling water on the surface).
- Apply an evaporation retarder between finishing passes.
- Dampen the subgrade and forms beforehand; cool the mix where practical.
- Start curing promptly once finishing is done.
High evaporation days also shorten the saw-cut window — plan your layout ahead with the concrete joint layout calculator and read when to saw cut concrete.
Pairs with the rest of your pour planning
The evaporation calculator lives alongside the other free concrete calculators and the joint layout calculator, so volume, saw cut schedule, and curing conditions all sit on the same job — saved together in your concrete Project File.
Informational planning tool only. Curing decisions, code compliance, and final specifications remain the responsibility of the licensed contractor or engineer of record.
Frequently asked questions
- How do I calculate concrete evaporation rate?
- Enter air temperature, concrete temperature, relative humidity, and wind speed. MudHub converts to metric and runs the ACI 305 nomograph equation, then shows the rate in lb/ft²/hr or kg/m²/hr.
- What is the ACI 305 evaporation equation?
- E = 5 × [(Tc + 18)^2.5 − r × (Ta + 18)^2.5] × (V + 4) × 10^-6, where Tc is concrete temperature in °C, Ta is air temperature in °C, r is relative humidity as a decimal, V is wind speed in km/h, and E is in kg/m²/hr.
- What evaporation rate is too high for concrete?
- ACI 305 guidance flags about 0.2 lb/ft²/hr (1.0 kg/m²/hr) as the point where plastic shrinkage cracking becomes likely and precautions are recommended. Low-bleed mixes can need precautions at lower rates.
- What causes plastic shrinkage cracking?
- Water leaving the surface faster than bleed water replaces it. The top dries and shrinks while the concrete below has not, so shallow cracks open before the concrete sets.
- Does wind increase concrete evaporation?
- Yes, strongly. At 85°F air and concrete with 30% humidity, the estimated rate goes from about 0.04 lb/ft²/hr with no wind to about 0.22 at 10 mph and 0.40 at 20 mph.
- Does humidity affect concrete evaporation?
- Yes. Drier air pulls moisture off the surface faster, so lower relative humidity raises the rate when everything else stays the same.
- Can I save the weather conditions with the project?
- Yes. Save the result to a project and MudHub keeps the original inputs and imported weather, so you have a record of the conditions on pour day.