🕐 Concrete Curing Time Calculator
Every other calculator here answers how much. This one answers when. Enter the cement type and the average temperature while the pour cures, and get the days to walk on it, to strip the forms, and to load it — with the reason the schedule moves with the weather.
🕐 Work Out Your Curing Schedule
Concrete counts warmth, not days
“Seven days for 70 percent, twenty-eight for full strength” is the figure everyone on site knows, and it is true — at about 20 °C. It is the temperature that goes unsaid, and it is the reason the same mix behaves like a different material in February.
Concrete gains strength by hydration, a chemical reaction between cement and water. Reactions run on temperature. The maturity method, standardised as ASTM C1074, makes that concrete: it adds up degrees above a datum for every hour of curing, producing an equivalent age at the 20 °C reference. A day at 5 °C is worth half a day. A day at 35 °C is worth one and a half.
That equivalent age then goes into the ACI 209R strength curve, which gives the share of the specified 28-day strength reached so far, with a different curve for ordinary Portland, rapid-hardening, and blended cements. The two together turn the weather into a programme.
The one figure worth reading twice is 70% of the specified strength — the long-standing threshold for striking supporting formwork and loading the member. It is where the cost of being wrong stops being a delay and starts being a failure, which is exactly why it belongs to your engineer and to test cylinders rather than to any calculator, this one included.
❓ Frequently Asked Questions
How long does concrete take to cure?
The honest answer is that it depends on temperature, not on the calendar. The familiar figures — 70% of the specified strength at 7 days, 100% at 28 — are for concrete held at about 20 °C. Hydration is a chemical reaction, and like any reaction it runs slower when it is cold. The same mix that reaches 70% in 7 days at 20 °C needs about 10 and a half days at 10 °C, and around 14 days at 5 °C. In a hot week it arrives sooner. This calculator converts the temperature you actually have into the schedule you actually get.
When can I remove the formwork?
Two very different answers, because formwork does two different jobs. Vertical forms on walls and columns carry no load once the concrete stands up on its own, and commonly come off within a day. Supporting formwork under a slab or beam holds the member up until it can hold itself, and the long-standing threshold for striking it is 70% of the specified 28-day strength. That is the figure the calculator highlights. It must be confirmed by your engineer and by test cylinders — the calculator tells you roughly when to book the crew, not when it is safe to strike.
What is the maturity method?
Concrete does not count days, it counts warmth over time. The maturity method, standardised as ASTM C1074, adds up the degrees above a datum temperature for every hour the concrete has been curing, which gives a single number that predicts strength far better than age alone. The version used here, Nurse-Saul, takes a datum of −10 °C and converts your site temperature into equivalent days at 20 °C: a day at 5 °C counts as half a day, a day at 35 °C as one and a half. It is why two identical pours, one in January and one in July, are ready weeks apart.
Can I pour concrete in cold weather?
Yes, with protection, and the rules are in ACI 306. Below about 5 °C strength gain slows to a crawl, and fresh concrete that actually freezes in its first day suffers permanent damage — the expanding ice disrupts the paste before it has the strength to resist, and that strength never comes back. Insulated blankets, heated enclosures, heated mixing water, and accelerating admixtures all help. What does not help is waiting: without protection the concrete is not slowly getting there, it has largely stopped.
Does hot weather make concrete stronger, since it cures faster?
No — and this catches people out, because the early days look excellent. Concrete cured hot gains strength quickly at first but reaches a LOWER ultimate strength than the same mix cured cool. The rapid early hydration builds a coarser, less uniform paste structure that limits the final result, an effect known as crossover. Hot weather also brings plastic shrinkage cracking as the surface dries faster than bleed water can reach it. ACI 305 covers the precautions: cool the mix, pour early or late in the day, and keep the surface wet.
Are these curing times exact?
They are planning figures, and two things limit them. The strength curve is ACI 209R's model for moist-cured concrete, which describes typical behaviour rather than your particular mix — admixtures, water-cement ratio, and cement fineness all shift it. And the maturity method assumes the concrete stays moist; concrete allowed to dry out stops gaining strength regardless of temperature. On a real job the authority is field-cured test cylinders, kept beside the pour in the same weather, broken in a lab. Use this to plan the programme and to understand why the schedule moves with the season.