Concrete Strength Estimate Calculator

Work out concrete strength estimate instantly with clear inputs, formula shown and shareable results.

About Concrete Strength Estimate Calculator

The ACI maturity relation fc(t) = fc28 x t / (a + b t) describes strength gain with age, where a and b depend on cement type and curing method. For Type I moist-cured concrete, a = 4 and b = 0.85, which reproduces the familiar milestones of roughly 45 percent at three days and 65 percent at seven.

Formula

Strength gain

fc(t) = fc28 x t / (a + b x t)

a: 4 Type I moist, 2.3 Type III moist, 1.0 steam cured
b: 0.85, 0.92 and 0.95 respectively

Worked example

With the default values below, Concrete Strength Estimate Calculator returns Estimated strength at this age of 17.59. Change any input above and every figure here is recalculated in your browser.

Inputs used

Design 28 day strengthminimum 1 MPa: 25 MPa
Age of concreteminimum 0.5 days: 7 days
Cement and curingone of Type I, moist cured, Type III rapid hardening, moist cured, Type I, steam cured: Type I, moist cured

Results

Estimated strength at this age: 17.59 MPa
Percentage of 28 day strength: 70.4% %
Estimated 3 day strength: 11.45 MPa
Estimated 7 day strength: 17.59 MPa

Step by step

1Values used
2Strength gain
3Estimated strength at this age= 17.59 MPa
4Percentage of 28 day strength= 70.4 %
5Estimated 3 day strength= 11.45 MPa
6Estimated 7 day strength= 17.59 MPa

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Do not use for formwork striking or load application decisions; rely on tested cube or cylinder strengths.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Do not use for formwork striking or load application decisions; rely on tested cube or cylinder strengths.

Frequently Asked Questions

How is the Concrete Strength Estimate figure worked out?

fc(t) = fc28 x t / (a + b x t). The ACI maturity relation fc(t) = fc28 x t / (a + b t) describes strength gain with age, where a and b depend on cement type and curing method.

Can I strike formwork on this estimate?

No. Formwork removal must be justified by actual cube or in-situ tests, or by code-specified minimum periods. The relation is for planning only.

What values do I need to enter?

This calculator takes 3 inputs: Design 28 day strength, Age of concrete, Cement and curing. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.