20 mm rebar: how much do you need

    Enter the dimensions of any concrete element - slab, footing, beam or column - and get the total reinforcement steel weight in kg, bar count and total length. Covers bar diameter, spacing, concrete cover and lap splices.

    This page opens with 20 mm already chosen, so nothing has to be hunted for in the list. Weight per meter goes with the square of the diameter, so a 20 mm bar weighs more than ten times what a 6 mm one does. This page opens the calculator with 20 mm already selected, so only the remaining fields are left to fill in. Change the other fields to your own numbers and press the button; the formula appears under the answer.

    Parameters

    Enter data for calculations

    The element type determines the reinforcement calculation method.

    Length of the element. For columns: vertical height.

    Width of the element or cross-section side.

    Slab thickness or cross-section height. For columns: the other side.

    Select the diameter of the main bars.

    Cover affects the effective bar length.

    Splice added when the element is longer than a standard bar (usually 6 m or 12 m).

    Optional - calculates estimated steel cost.

    Form progress0 / 5 fields

    💡 Fill in all required fields to unlock the calculate button

    Reinforcement steel for any concrete element - weight, bars and cost

    Four element types in one tool: slabs (foundations, floors, terraces), strip footings, beams (ring beams, lintels) and columns. Enter the dimensions, bar diameter and spacing - the calculator returns the total steel weight in kg, bar count, total length and cost estimate. For slabs it computes a mesh grid in one or two directions. For footings, beams and columns it separates main bars from stirrups.

    How to use the rebar calculator - step by step

    1. Element type - slab, strip footing, beam or column. This determines whether the tool calculates mesh (slabs) or main bars + stirrups (linear elements).
    2. Dimensions - length, width and thickness/height in meters. For columns, length = vertical height.
    3. Bar diameter - from 6 mm (mesh, stirrups) to 25 mm (heavy foundations). Weight per meter is looked up from the EN 10080 table automatically.
    4. Spacing - bar spacing for slabs (mesh), stirrup spacing for linear elements. Typical slab mesh: 15 cm. Typical stirrups: 20 cm.
    5. Concrete cover - minimum distance from bar to concrete surface. Foundation in ground: 4-5 cm, internal slab: 2-3 cm.
    6. Lap splice - overlap when joining bars (typically 30-50x diameter). Enter 0 for short elements.
    7. Read the results - total steel weight, bar count, total length, kg per m2 (slabs) or kg per running meter (linear elements), and estimated cost.

    Rebar weight per meter - EN 10080 reference

    Steel reinforcement is sold by weight (per ton or per kg). Knowing the weight per meter for each bar diameter lets you convert from a bar schedule into a purchase order.

    Diameter kg/m m per ton Cross-section (mm2)
    6 mm0.2224,50528.3
    8 mm0.3952,53250.3
    10 mm0.6171,62178.5
    12 mm0.8881,126113.1
    16 mm1.578634201.1
    20 mm2.466405314.2
    25 mm3.853260490.9

    Practical examples

    Example 1: Garage slab 6 x 4 m, 15 cm thick, 10 mm bars at 15 cm, 2-way mesh, 4 cm cover
    Result: 197.8 kg of steel, 68 bars, total length 320.6 m, 8.2 kg/m2
    Example 2: Foundation slab 10 x 8 m, 25 cm thick, 12 mm bars at 15 cm, 2-way mesh, 5 cm cover
    Result: 944.7 kg of steel, 121 bars, 11.8 kg/m2
    Example 3: Strip footing 12 m long, cross-section 0.4 x 0.5 m, 4 x 12 mm main bars, 6 mm stirrups at 20 cm
    Result: 65.1 kg total (42.3 kg main bars + 22.8 kg stirrups), 5.4 kg/m
    Example 4: Ring beam 8 m long, cross-section 0.25 x 0.25 m, 4 x 12 mm main bars, 6 mm stirrups at 15 cm
    Result: 38.7 kg total (28.1 kg main + 10.5 kg stirrups)
    Example 5: Column 3 m tall, cross-section 0.30 x 0.30 m, 4 x 16 mm main bars, 8 mm stirrups at 20 cm
    Result: 25.3 kg total (18.4 kg main + 6.8 kg stirrups)

    FAQ - Frequently asked questions

    How much rebar do I need per m2 of slab?
    For a typical residential slab with 10 mm bars at 15 cm spacing in two directions, expect about 1.8-2.5 kg/m2. With 12 mm bars at 15 cm, this rises to 2.5-3.5 kg/m2. The exact value depends on concrete cover and element size.
    What concrete cover should I use?
    Foundations in ground: 4-5 cm. Internal slabs/beams: 2-3 cm. External exposed concrete: 3-4 cm. Columns: 3-4 cm. Cover protects rebar from corrosion - insufficient cover is one of the most common causes of concrete deterioration.
    What is a lap splice and how long should it be?
    A lap splice is the overlap where two bars meet. The standard length is 30-50 times the bar diameter. For a 12 mm bar: 12 x 40 = 480 mm (48 cm). Splices are needed when the element is longer than a standard bar (usually 6 m or 12 m).
    What bar diameter should I use for a house foundation slab?
    Most residential foundation slabs use 10 mm or 12 mm bars at 15-20 cm spacing in both directions. The structural engineer specifies the exact diameter and spacing based on soil bearing capacity and building loads.
    Why does the calculator show stirrups for beams but not for slabs?
    Slabs resist loads primarily through bending in one or two directions - a mesh of bars handles this. Beams, footings and columns also resist shear forces, which require transverse reinforcement (stirrups or ties) to prevent diagonal cracking.
    Is this calculator a substitute for a structural engineer?
    No. This tool provides a material estimate for purchasing and budgeting. The actual reinforcement layout, bar diameter, spacing and detailing must come from a structural design by a licensed engineer based on the specific loads, soil conditions and building codes applicable to your project.

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    See also

    Rebar for a plyta - Length, Weight and CostRebar for a lawa - Length, Weight and CostRebar for a belka - Length, Weight and CostRebar for a slup - Length, Weight and Cost6 Rebar - Weight per Meter and Total8 Rebar - Weight per Meter and Total10 Rebar - Weight per Meter and Total12 Rebar - Weight per Meter and Total16 Rebar - Weight per Meter and Total25 Rebar - Weight per Meter and Total

    Calculator verified by the LiczGrupa.pl team

    Content, formulas and results have been reviewed for accuracy and relevance by our team of specialists.

    Patryk Matyjasik

    Reviewed by: Patryk Matyjasik

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