SettingsSettings for this calculationUS
The temperature of the fresh concrete, not the air.
Measure with a probe thermometer in the mix shortly after placement — fresh concrete is often several degrees warmer than the surrounding air due to the hydration reaction.
The ambient air temperature at the job site.
Use the actual expected temperature during the pour and initial cure, not a daily average.
The relative humidity at the job site.
Lower humidity dramatically increases evaporation risk — arid climates need extra vigilance even at moderate temperatures.
The wind speed across the concrete surface during placement and finishing.
Wind speed has an outsized effect on evaporation rate — even a moderate breeze across a large slab pour can push evaporation rate well past the critical threshold.
Estimated evaporation rate
0.11 lb/ft²/hr
Below the critical threshold under these conditions — standard curing practices should be adequate, though conditions can change during a long pour, so re-check if temperature or wind picks up.
- Critical threshold
- 0.2 lb/ft²/hr
They open the calculator with your figures already in it
Concrete Evaporation Rate Calculator: 0.11 lb/ft²/hr — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- ACI 305R / Uno metric evaporation equation: E = 5 x ([Tc+18]^2.5 - r x [Ta+18]^2.5) x (V+4) x 10^-6, with E in kg/m2/h, temperatures in degrees C and wind speed in km/h
- Widely cited critical threshold: evaporation rate at or above approximately 0.2 lb/sq ft/hr (1.0 kg/m²/hr) significantly raises the risk of plastic shrinkage cracking
Inputs used
- Concrete Temperature
- 77 °F
- Air Temperature
- 68 °F
- Relative Humidity (%)
- 50
- Wind Speed (km/h)
- 10
Intermediate steps
- Critical threshold
- 0.2 lb/ft²/hr
Confidence note: Below the critical threshold under these conditions — standard curing practices should be adequate, though conditions can change during a long pour, so re-check if temperature or wind picks up.
What this calculation does not cover
- Solar gain is not in the model. The equation reads concrete temperature, air temperature, humidity and wind only, so a slab in full sun and the same slab in shade return an identical rate from identical readings. If the sun is on the pour, take the concrete temperature off the finished surface rather than off the chute, or the answer comes back low.
- Bleed rate is not modelled. Plastic shrinkage cracking is evaporation outrunning the bleed water rising to replace it, and this calculates only the evaporation half. Low-bleed mixes - low water-cement ratio, silica fume, heavy fly ash replacement, high-range water reducers - can crack plastically at rates below the threshold this page flags.
- Nothing about the slab itself is an input. Thickness, subgrade moisture and absorption, restraint from reinforcement and edge conditions, finishing timing, and the curing method actually applied all govern whether cracks form, and none of them reach the calculation.
- This is one moment at one spot. Wind, humidity and temperature move across the hours of a placement and vary across a large slab - funnelled between buildings, faster over a hot deck, calmer behind a windbreak. Re-run it against readings taken at slab level during the pour, not against a forecast from the nearest airport.
- The threshold is a screening line, not a pass/fail verdict and not a curing specification. A rate below it is not a guarantee against cracking and a rate above it is not a prediction of it; the number tells you when to have fogging, evaporation retardant and windbreaks ready, and it does not replace the hot- or cold-weather concreting requirements in your project specification or the supplier's guidance for the mix being placed.
Add the equipment this sizes
This result is a specification — 0.11 lb/ft²/hr — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-03 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations2
- ACI 305R / Uno metric evaporation equation: E = 5 x ([Tc+18]^2.5 - r x [Ta+18]^2.5) x (V+4) x 10^-6, with E in kg/m2/h, temperatures in degrees C and wind speed in km/h
- Widely cited critical threshold: evaporation rate at or above approximately 0.2 lb/sq ft/hr (1.0 kg/m²/hr) significantly raises the risk of plastic shrinkage cracking
Which documents these citations point at
Standards referenced: ACI 305R (American Concrete Institute, United States).
Cite this page
Your workspace
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Tools and safety for this job
To place and finish concrete, erect formwork and saw-cut cured concrete. Generic types, no brands, no prices.
Protection this work requires
- Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
- Hardwood dust is a recognised carcinogen: extract at the tool and wear a P2/N95 respirator when cutting or sanding indoors.
- Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
- Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
- Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
- Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
Show the 17 tools this job needsHide tools
Essential
Angle grinder
Bull float and edger
Circular saw
Claw hammer
Dust extractor or vacuum with a fine filter
Screed bar or rail
Shovel and spade
Spirit level
String line and pins
Tape measure
Wheelbarrow
Recommended
Chalk line
Cordless drill/driver
Floor or cut-off saw
Plate compactor
SDS rotary hammer
Optional
Power float
Also needed as materials: chalk refill, circular saw blades, cutting and diamond discs, diamond blades, drill and driver bits, SDS bits and chisels.
what each concrete tool is for, and the spec that decides which to buy where one does.
Conditions are favorable for a standard cure, but evaporation risk can change quickly if wind picks up or humidity drops during a long pour — recheck this calculator against updated conditions if the placement runs long.