Free Reinforced Concrete Calculator

Analyse an RC beam or column design in accordance with Eurocode 2 with this rebar calculator.

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Theory & FAQ

Concrete section profile

Concrete Strength f_ck MPa

Enter strength more than 0 & less than 60MPa.

Section width mm

Enter width more than 0 & less than 3000mm.

Section depth mm

Enter depth more than 0 & less than 3000mm.

Applied loading

Bending M_ed,y kNm

Enter moment greater than 0.

Axial N_ed kN

Only axial compression is considered.

Bottom reinforcement

No. bars

Bar diameter mm

Cover (to bottom) mm

Enter cover greater than 0 & less than depth/2

Advanced settings:

Shear V_ed kN

Enter shear greater than 0.

Specify the top reinforcement

No. bars

Bar diameter mm

Cover (to top) mm

Enter cover greater than 0 & less than depth/2

4. Reinforcement properties:

Steel strength f_yk MPa

Enter strength greater than 0 & less than 700MPa

Cover to edges mm

Enter cover greater than 0 & less than width/2

Advanced settings

Reinforcement spacing

Top bar spacing: mm

Bottom bar spacing: mm

Minimum allowable top bar spacing: mm

Minimum allowable bottom bar spacing: mm

Reinforcement area

Reinforcement area top: mm²

Reinforcement area bottom: mm²

Total reinforcement: mm² (%)

Min reinforcement limit: mm² (%)

Max reinforcement limit: mm² (%)

Result

ULS %

SLS %

Warnings:

❌ Top bars seem too close.

❌ Bottom bars seem too close.

❌ Cover to the top seems too little, try >30mm.

❌ Cover to the bottom seems too little, try >30mm.

❌ Cover to the sides seems too little, try >30mm.

❌ Check your reinforcement area is within max & min limits.

d mm	x mm	e_s1	e_s2	σ'_s1 N/mm²	σ'_s2 N/mm²	M₁ Nmm	M₂ Nmm	M₃ Nmm	M kNm	N kNm

Calculation Results

Ultimate limit state

ULS result
M-N utilisation	%
Shear analysis

Serviceability limit state

SLS result
Neutral Axis Depth	mm
Assumed crack limit	0.3mm
Short term crack width	mm
Long term crack width	mm

Method & theory

How the concrete section is checked

The section is checked against Eurocode 2: for each neutral-axis position the axial and bending resistance is calculated, tracing out a capacity envelope, then shear link area and short/long-term crack widths are checked against the applied ultimate and serviceability design forces.

Watch how it works

What's this calculator used for?

This free calculator can be used by Civil Engineers to design reinforced concrete. This tool can be used to calculate reinforcement and rebar areas and calculate bar spacings are correct against the European regulations (Eurocode 2). Calculate the neutral axis of a reinforced concrete beams and used it to determine the tension and compression stresses resulting from the bending moment. Design the shear reinforcement and check that concrete short term and long term crack widths comply with servicibility limit state.

Common questions

Concrete’s strength, cost and availability has made it the most widely used construction materials of the 21st century. Concrete is made from cement mixed with water. Often stone aggregate and chemical admixtures are added to the mix to improve the material structural performance and workability. The most common mix of cement, aggregates and water used is in the ratio 1:2:4.

Concrete is weak in tension and shear. Steel reinforcement forms a bond with concrete and provides concrete with tensile strength, prevent dangerous brittle failure of the material. Brittle failure is dangerous in unreinforced concrete as occurs suddenly and provides no warning that the material is about to fail.

When a beam flexes one face of the beam experiences tensile stress and the other experiences compressive stress. A neutral axis forms, along which line the stress is zero. The neutral axis position depends on the position and specification of any steel reinforcement and the nature of the applied load.

Each neutral axis position within the concrete section will have a resulting axial and bending resistance. Plotting the axial resistance against the bending resistance for each neutral axis position creates an envelope which represents the capacity of the concrete section.

Shear links are used to resist shear force applied to concrete. The concrete strut capacity equation is used to determine the area of shear links required to provide the necessary shear link resistance.

A minimum reinforcement area of 0.24% of the concrete section area should be provided as a typical value.
In order to provide crack control and satisfy SLS requirements a minimum area of reinforcement must be provided to concrete. The amount can be estimated from an equilibrium equation between the tensile force in concrete before cracking and the tensile force in reinforcement at yielding.
Minimum reinforced concrete steel area can be calculated with the equation
As,mín·σs = kc · k · fct,eff · Act
Where As,min is equivalent to the minimum area required within the tensile zone.
Act is the area of concrete within the tensile zone.
σs is the stress in the steel after crack formation, this can be taken as the yield strength of the steel
fct,eff is the tensile strength of the concrete
k is the coefficient which allows for the effect of non-uniform self-equilibrating stresses, which lead to a reduction of restraint forces
= 1,0 for webs with h ≤ 300 mm or flanges with widths less than 300 mm
= 0,65 for webs with h ≥ 800 mm or flanges with widths greater than 800 mm
kc is a coefficient which takes account of the stress distribution within the section immediately prior to cracking and of the change of the lever arm:
For pure tension kc can be taken as = 1,0, this can also be used for all cases as a conservative value.

A maximum of between 1% and 2% of the concrete area should be provided as reinforcement

The minimum spacing between bars should be greater than the bar size, the maximum aggregate size + 5mm, or 20mm according to Eurocode 2 (EC2)
The minimum horizontal spacing between bars should be greater than the bar size or the maximum aggregate size + 5mm. The minimum vertical spacing between bars should be greater than the bar size or 2/3 of the maximum aggregate size according to BS8110

The compressive stress in the concrete shall be limited in order to avoid longitudinal cracks, micro-cracks or high levels of creep, where they could result in unacceptable effects on the function of the structure.

Longitudinal cracks may occur if the stress level under the characteristic combination of loads exceeds a critical value. Such cracking may lead to a reduction of durability. In the absence of other measures, such as an increase in the cover to reinforcement in the compressive zone or confinement by transverse reinforcement, it may be appropriate to limit the compressive stress to a lower value for concrete exposed to harsh exposure conditions.

Concrete column capacity charts can be used to calculate the reinforcement area requirements from height, width and the applied axial force and bending.

Calculation validation