Concrete Curing Time Chart: Days to Strength by Temp 2026

Cold weather triples the wait

Concrete does not dry — it cures. The cement reacts with water in a chemical reaction called hydration, and that reaction builds strength over days and weeks. The warmer the concrete, the faster the reaction: at 70°F a standard mix reaches 70% of its 28-day design strength in 7 days, but at 40°F the same strength takes 21 days — three times as long. Below 40°F the reaction effectively stops, and water in the fresh concrete can freeze and crack it. The chart gives typical days to 50%, 70% and 100% of design strength at curing temperatures from 40°F to 80°F, per ACI 308 curing guidance, for a standard mix (water-cement ratio about 0.50). On the defaults — curing temperature 70°F, target strength 70% — the answer is 7 days; walk on after 3 days, drive on after 7 days.

At the defaults — curing temperature 70°F, target strength 70% — the days to target strength are 7, the walk-on days are 3 and the drive-on days are 7. Check the identities: days to target = the table value at the curing temperature, interpolated between rows; walk-on days = days to 50% strength at the same temperature; drive-on days = days to 70% strength at the same temperature. Between rows the days are interpolated linearly — at 65°F, halfway between the 60°F and 70°F rows, 70% takes 8.5 days. Above 80°F the 70/80°F slope is extrapolated up to 90°F; below 40°F the answer is —, curing effectively stops. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

The worked example, line by line

Setup: curing temperature 70°F, target strength 70%.

Line 1 — the days. 70°F is a table row, so the 70% column reads 7 days exactly — no interpolation needed.

Line 2 — walk on. The 50% column at 70°F reads 3 days — the slab is strong enough to walk on after 3 days.

Line 3 — drive on. The 70% column at 70°F reads 7 days — the slab is strong enough for a car after 7 days.

Line 4 — full strength. The 100% column at 70°F reads 28 days — the design strength the mix is sold by.

Line 5 — the cold check. At 40°F the same 70% takes 21 days — three times as long — and below 40°F the answer is —: curing effectively stops, so protect the slab from freezing.

Reverse: the temperature for 7 days at 70% strength is 70°F; at that temperature the days are 7. The temperature for 10 days at 70% is 60°F; at that temperature the days are 10. The temperature for 3 days at 50% is 70°F; at that temperature the days are 3. The temperature for 28 days at 100% is 70°F; at that temperature the days are 28.

Every branch, checked

50°F, target 70%: 14 days to 70% strength (walk-on 6 days, drive-on 14 days). At 50°F the concrete takes 14 days to reach 70% strength — twice as long as at 70°F. Walk on after 6 days, drive on after 14.

60°F, target 70%: 10 days to 70% strength (walk-on 4 days, drive-on 10 days). At 60°F it takes 10 days to reach 70% strength. Walk on after 4 days, drive on after 10.

80°F, target 70%: 5 days to 70% strength (walk-on 2 days, drive-on 5 days). At 80°F it takes 5 days to reach 70% strength. Walk on after 2 days, drive on after 5.

65°F, target 70%: 8.5 days to 70% strength (walk-on 3.5 days, drive-on 8.5 days). At 65°F, halfway between the 60°F and 70°F rows, it takes 8.5 days to reach 70% strength — the interpolation between 10 and 7 days.

55°F, target 70%: 12 days to 70% strength (walk-on 5 days, drive-on 12 days). At 55°F it takes 12 days to reach 70% strength — halfway between 14 days at 50°F and 10 days at 60°F.

45°F, target 50%: 7.5 days to 50% strength (walk-on 7.5 days, drive-on 17.5 days). At 45°F, target 50%, it takes 7.5 days to reach half strength — halfway between 9 days at 40°F and 6 days at 50°F.

70°F, target 50%: 3 days to 50% strength (walk-on 3 days, drive-on 7 days). At 70°F, target 50%, it takes 3 days to reach half strength — you can walk on the slab after 3 days.

70°F, target 100%: 28 days to 100% strength (walk-on 3 days, drive-on 7 days). At 70°F, target 100%, it takes 28 days to reach full strength — the 28-day design strength the mix is sold by.

75°F, target 70%: 6 days to 70% strength (walk-on 2.5 days, drive-on 6 days). At 75°F it takes 6 days to reach 70% strength — halfway between 7 days at 70°F and 5 days at 80°F.

85°F, target 70%: 4 days to 70% strength (walk-on 1.5 days, drive-on 4 days). At 85°F it takes 4 days to reach 70% strength — extrapolating the 70/80°F slope past the top row.

90°F, target 70%: 3 days to 70% strength (walk-on 1 days, drive-on 3 days). At 90°F it takes 3 days to reach 70% strength — the top of the extrapolation, and the cap: hotter than 90°F is clamped to 90°F.

72°F, target 70%: 6.6 days to 70% strength (walk-on 2.8 days, drive-on 6.6 days). At 72°F it takes 6.6 days to reach 70% strength — a fifth of the way from 7 days at 70°F toward 5 days at 80°F.

90°F, target 100%: 14 days to 100% strength (walk-on 1 days, drive-on 3 days). At 90°F, target 100%, it takes 14 days to reach full strength — extrapolating the 70/80°F slope for full strength.

68°F, target 100%: 29.4 days to 100% strength (walk-on 3.2 days, drive-on 7.6 days). At 68°F, target 100%, it takes 29.4 days to reach full strength — a fifth of the way from 28 days at 70°F toward 35 days at 60°F.

What the defaults assume

The model assumes a standard mix with a water-cement ratio of about 0.50, cured per ACI 308 guidance — kept moist and at temperature. It assumes the curing temperature is the average temperature over the first days, not a single reading: a slab poured at 70°F that drops to 45°F overnight cures slower than the 70°F row says. It assumes no accelerators, retarders or supplementary cementitious materials — admixtures shift every number. It assumes the concrete is kept moist: drying out stops hydration the same way cold does. With a curing temperature of 32°F the answer is — (curing effectively stops). With 35°F the answer is —. With 39°F the answer is —. With 40°F and a 70% target the answer is 21 days. With 100°F the temperature is clamped to 90°F and the answer is 3 days at 70%. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures (8.5, 7.5, 6.6, 29.4 days) are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The homeowner pouring a driveway in June at 70°F: they learn the slab takes 7 days to reach 70% strength — walk on after 3 days, drive on after 7 — and they check the 80°F branch (5 days) to see what a hot week would save.
• The contractor pouring a slab in November at 50°F: they learn 70% takes 14 days — twice as long as at 70°F — and they check the 40°F branch (21 days) before promising the client a drive-on date.
• The DIYer pouring a patio at 45°F: they learn half strength takes 7.5 days — and they check the 32°F edge (—) to see why the slab needs blankets, not just patience.
• The builder planning a pour at 90°F: they learn 70% takes 3 days — but full strength still takes 14 days — and they check the 85°F branch (4 days) to see how the heat trades speed against cracking risk.

Accuracy & limitations

The math is exact arithmetic on your two inputs: days to target = the table value at the curing temperature, interpolated linearly between rows; walk-on days = days to 50% strength at the same temperature; drive-on days = days to 70% strength at the same temperature. The 1-decimal exact is shown where the interpolation matters: at 65°F the 70% time is 8.5 days; at 45°F the 50% time is 7.5 days; at 72°F the 70% time is 6.6 days; at 68°F the 100% time is 29.4 days. What the model cannot do is certify your slab: the values are typical for a standard mix per ACI 308 curing guidance, not a mix-design guarantee — your mix, your admixtures and your weather all move the numbers. For the mix itself, see the concrete mix calculator; for bag counts, see the concrete bag chart; for block work on the same job, see the concrete block size chart; for the joists above the slab, see the joist span chart; for the drywall inside, see the drywall screw spacing chart. This is a chart, not engineering advice.