Lintel Beam Steel Calculator
Calculate steel rebar requirements — main bars, stirrups, and total kg — for lintel beams.
By Syed Mubashir Ali · Last updated
Reading the structural drawing first
Before touching this calculator, read the drawing properly: beam mark, section dimensions, concrete grade, main bar diameters and counts (top and bottom), stirrup diameter and spacing, and any notes on laps or curtailment. The calculator takes the span, section, main bars and stirrup diameter, and assumes the stirrup spacing and a 300mm lap at each end, so check those assumptions against the drawing. A misread drawing produces a confident wrong answer.
Pay particular attention to whether bars are straight or bent up, and where laps are permitted. Laps add length (a 12m bar with a 600mm lap is effectively 11.4m of beam) and the lap positions affect how many bars you actually need to order.
Ordering steel without waste
Order against the total cutting lengths, then convert to stock lengths with minimal offcuts. If your beams need many 4.2m bars, three come from a 12m stock length with 1.2m left over: plan whether that offcut serves as a link bar or becomes scrap, because scrap is money.
Check the delivery against the BBS before the steel fixer starts: diameters with a tape, counts by bundle tags. Wrong-diameter bars get built in remarkably fast, and pulling them out of cast concrete is not a conversation anyone enjoys.
How to Use Lintel Beam Calculator
- 1This is a steel quantity take-off, not a structural design. The section size and reinforcement must come from a qualified structural engineer.
- 2Enter the span in metres or feet, and the beam width and depth in millimetres.
- 3Choose the main bar diameter (10, 12, 16, 20 or 25mm) and the number of main bars.
- 4Choose the stirrup diameter: 8, 10 or 12mm.
- 5Calculate to get the steel quantities for the section you have been given.
- 6Cross-check the output against the bar bending schedule. The BBS is the authoritative document: if this calculator and the BBS disagree, the BBS wins and you should find out why before ordering.
- 7Round bar lengths up to standard stock lengths when ordering. Rebar comes in standard lengths (commonly 12m); the calculator gives total bar length and weight, and your supplier cuts or you lap to suit.
Frequently Asked Questions
Does this design the beam for me?
No, and it must not be used that way. It counts steel for a section someone else has designed. Beam sizing and reinforcement depend on loads, spans, support conditions, concrete grade and code requirements, and getting them wrong causes structural failure. That is a job for a qualified structural engineer.
What is it actually for?
Take-off and ordering. Once an engineer has specified the section and reinforcement, you still need the bar quantities and lengths to order steel and check what arrives. That is arithmetic, and this does it quickly.
Does it include laps, bends and cover?
It calculates from the dimensions and bar arrangement you enter. Laps, anchorage, bends and cover are detailing requirements that vary by code and by the engineer's drawing, so check the output against the bar bending schedule before ordering.
Can I use it for a lintel over a domestic opening?
For counting steel in a lintel that has been designed, yes. Even a domestic opening needs the lintel sized properly: removing or undersizing support over an opening in a loadbearing wall is one of the more common serious errors in home alterations, and it usually also needs building control approval.
Which stirrup spacing should I use?
Whatever the engineer specified. Shear reinforcement spacing typically varies along the span, closer near supports, and that comes from the design rather than from a rule of thumb.
What is a bar bending schedule?
A table listing every bar in the element: mark number, diameter, shape code, length, and quantity. It is what the steel fixer works from and what you order against. This calculator produces the quantities; the BBS organises them for fabrication and checking.
What steel grade should I specify?
That comes from the structural design, not from a calculator. Common grades are 500MPa deformed bar for main reinforcement in many codes. Using the wrong grade (or assuming one) changes the structural capacity, so take it from the engineer's specification.
How are stirrups spaced?
Spacing comes from the shear design and is shown on the structural drawings: commonly tighter near supports where shear is highest. For a quick estimate this tool assumes even spacing of half the beam depth, capped at 300mm. Your drawings will often show tighter spacing near supports, so recount from them before ordering.
About Lintel Beam Calculator
The Lintel and Beam Steel Calculator works out reinforcement quantities for a beam section you specify: span, width, depth, main bar diameter and count, and stirrup diameter. It runs entirely in your browser.
It is a quantity tool sitting downstream of a design. An engineer determines the section and the reinforcement from the loads, spans, support conditions and code; this converts that specification into steel you can order and check against a delivery.
Nothing here designs anything, and it should not be used to decide a beam size. Undersized or missing support over an opening in a loadbearing wall is among the more common serious errors in building work, and it is also typically a matter for building control approval. If you do not have an engineer's design, that is the next step rather than this calculator.
Check the output against the bar bending schedule before ordering. Laps, anchorage, bends and cover vary by code and by the specific drawing, and they affect the lengths you need.
Used properly, it removes the arithmetic errors that creep into manual take-offs: a missed bar, a wrong length multiplied across twenty beams. Those errors cost money at best and cause site delays at worst. What it cannot do is replace the engineering judgement that produced the section in the first place, and it never pretends to.