Bar Bending Schedule (BBS): Cutting Length, Hooks and Bend Deductions

Every steel bar in a reinforced concrete house is cut to a length that somebody wrote down first, and that written list is the bar bending schedule. A bar bending schedule (BBS) lists each bar by its mark, diameter, number, cutting length and bent shape, so the bar bender can cut and bend without reading the drawing, and the totals give the kilograms of steel to order.

The schedule is prepared by the structural engineer or a detailer working from the structural drawings. The format and the allowances for hooks and bends come from IS 2502 : 1963, the Bureau of Indian Standards code of practice for bending and fixing of bars. The development lengths and laps that set how long the bars run come from IS 456 : 2000, the concrete code.

This guide explains how to read one and how the cutting lengths are worked out, with four worked examples: a footing mat, a column bar, a beam stirrup and a slab crank bar. It carries no rupee figures. Steel rates change every month; the method below does not.

What does a bar bending schedule contain?

IS 2502 Table I sets out the standard form, and it has eight columns. They are the location (for example “Column C4”), the bar mark, the size and type of steel, two count columns (the number of members and the number of bars in each), the total number of bars, the length of each bar, and a sketch of its shape with the bending dimensions.

The bar mark is a short label that goes on a tag tied to the bundle. IS 2502 asks for it to stay simple, and clause 9.1.2 asks that every bundle of bent bars carry a label with the bar mark, the schedule reference number and its position in laying. On site, that tag is what stops a 12 mm beam bar going into a column.

SP 34 : 1987, the BIS handbook on concrete reinforcement and detailing, asks in Section 5 for the total length of each bar type, details of bar chairs and a remarks column for laps and special notes. Most Indian schedules also add the weight per metre and the total weight. A typical row looks like this.

That row is the footing worked out further down this page. One line per bar shape per member, then a summary at the foot of the sheet adding up the weight for each diameter, is all a BBS is.

How do you calculate cutting length in a BBS?

The cutting length is the length of straight bar you cut from the 12 metre stock before bending. The rule is short:

Cutting length = sum of the straight dimensions shown on the sketch + hook allowances + bend allowances − bend deductions

The dimensions on a BBS sketch are measured to the outside of the bar. When a bar is bent, it does not use up as much steel at the corner as the two outside dimensions suggest, because the bar curves round inside the corner. So a length is taken off for every bend. Hooks and anchorage legs need extra length, so that is added.

Two rules from IS 2502 finish the sum. Clause 5.1.1 says the cutting length is given to the next whole 25 mm above the calculated figure, so 1,652 mm is written as 1,675 mm. The same clause says any small excess goes into the end anchorage, not into the main span of the bar.

What are the hook and bend allowances in IS 2502?

IS 2502 ties both allowances to how tightly the bar is bent. The internal radius of a standard hook or bend is k times the bar diameter d, and k depends on the steel. SP 34 Table 4.1 gives k = 2 for mild steel and k = 4 for cold-worked steel, the class IS 1786 deformed bars belonged to when the handbook was written. TMT bars, the Fe 500 and Fe 500D bars sold for house construction, are made to IS 1786 today, so most engineers detail them at k = 4. A standard hook or 90 degree bend also ends in a straight length of at least 4d.

The note to Table II says each allowance is rounded to the nearest 5 mm and is never less than 75 mm. So a 10 mm TMT bar gets a hook allowance of 130 mm, and an 8 mm mild steel bar gets 75 mm, not 72.

These numbers are geometry. A semicircular hook bent round a radius of 4d, with its 4d straight end, uses about 13d of bar beyond the point where the dimension stops. A tight mild steel hook at radius 2d uses about 9d. That is also why the “hook = 9d” figure printed on many site sheets is a mild steel number. Used for a TMT main bar bent to SP 34’s radius, it cuts the bar short.

How much a hook is worth in the concrete is a separate question. IS 456 clause 26.2.2.1 counts a standard U-type hook as 16d of anchorage, and a bend as 4d for every 45 degrees, up to 16d.

What bend deductions are used for 45, 90 and 135 degrees?

Sites across India use one short table for the length taken off at each bend. It is a convention, not a clause of IS 2502, and it is printed on most BBS templates and calculators.

The 90 degree figure can be checked. Two outside dimensions meeting at a right angle each run past the start of the curve by the radius plus one bar diameter. The bar itself follows a quarter circle along its centre line. Work that out for an internal radius of 2d and the difference is 2.07d, which is where “2d” comes from. Bend the same bar round a 4d radius and the difference grows to about 2.9d.

The deduction depends on the bending pin as much as on the angle. That does not make the table wrong. It means the schedule should say which deductions it used, and the bar bender’s pin should match it. On a 12 mm bar the gap between the two radii is about a centimetre per bend.

How do you calculate the cutting length of a footing bar?

Take an isolated footing 1,500 × 1,500 mm (about 4 ft 11 in square) with 12 mm bars at 150 mm spacing both ways, each bar turned up 150 mm at both ends. IS 456 clause 26.4.2.2 sets the minimum cover for footings at 50 mm.

Straight length = 1,500 − 2 × 50 = 1,400 mm
Two upturned legs = 2 × 150 = 300 mm
Two 90° bend deductions = 2 × 2 × 12 = 48 mm
Cutting length = 1,400 + 300 − 48 = 1,652 mm, written as 1,675 mm

Number of bars one way = 1,400 ÷ 150 = 9.33, rounded up to 10 spaces, so 11 bars. Both ways, 22 bars.

Total length = 22 × 1.675 = 36.85 m. At d² ÷ 162 a 12 mm bar weighs 0.889 kg per metre, so the footing takes about 32.8 kg of steel. That weight formula and a table of bar weights by diameter are in the building material calculation guide.

How do you find the cutting length of a column bar?

A column bar has three parts: the foot that sits on the footing mat, the vertical run, and the lap left sticking up for the next floor’s bars.

Say the bar is 12 mm, has a 300 mm foot bent at 90 degrees, runs 3,500 mm from the top of the footing mat to just above the first floor slab, and the drawing asks for a 600 mm lap above that.

Cutting length = 300 + 3,500 + 600 − 2 × 12 = 4,376 mm, written as 4,400 mm

The 600 mm lap here is the figure on the example drawing. The real lap is set by the design, and IS 456 gives its floor. Clause 26.2.5.1 says a lap in compression is not less than the development length in compression and never under 24d. A lap in flexural tension is the development length or 30d, whichever is more. Bars larger than 36 mm are normally welded rather than lapped.

The development length itself is Ld = φσs ÷ 4τbd, where φ is the bar diameter, σs the stress in the bar and τbd the design bond stress. With IS 456’s bond stresses, raised 60% for deformed bars, it works out like this for a bar stressed to 0.87 fy:

SP 34 tabulates the same values bar by bar. A 12 mm Fe 500 bar in M20 concrete needs about 680 mm to develop in tension. That is why switching from Fe 415 to Fe 500 lengthens laps, even though it can reduce the number of bars.

How do you calculate the cutting length of a stirrup?

Take a 230 × 450 mm (about 9 × 18 inch) beam with 25 mm cover and 8 mm stirrups closed with two 135 degree hooks. IS 456 applies the nominal cover to links as well, so the stirrup’s outside dimensions are:

A = 230 − 2 × 25 = 180 mm
B = 450 − 2 × 25 = 400 mm

A closed stirrup has three 90 degree corners and two 135 degree bends where the hooks turn in. The usual site formula is:

Cutting length = 2(A + B) + 2 × hook length − 3 × 2d − 2 × 3d
= 2(180 + 400) + 2 × 80 − 48 − 48 = 1,224 mm, written as 1,225 mm

The hook length here is taken as 10d, 80 mm for an 8 mm bar. That figure is where site practice varies most: templates in use put a 135 degree stirrup hook anywhere from 9d to 12d. The code floor is the straight end. IS 456 clause 26.2.2.4 counts a stirrup as anchored when the bar is bent 135 degrees and runs at least 6d past the end of the curve, and IS 2502 clause 3.3 asks for at least 8d straight beyond the curve on binders and stirrups. Whatever hook length the schedule uses, the bent stirrup must still show that straight end.

The number of stirrups follows from the spacing on the drawing: the length of beam to be covered divided by the spacing, plus one. Beams usually carry closer stirrups near the supports, so count each zone separately.

How do you calculate a crank bar in a slab?

A crank, or bent-up, bar runs along the bottom of a slab at mid span and lifts to the top over the supports. Each lift is cut at 45 degrees, and the sloping part is longer than the flat distance it covers by 0.42 times the height of the crank.

That 0.42 is plain trigonometry. A 45 degree slope that rises by D runs √2 × D, which is 1.414D, while it covers only D horizontally. The extra is 0.414D, rounded to 0.42D.

For a 125 mm slab with 20 mm cover top and bottom and 10 mm bars, the crank height is 125 − 20 − 20 − 10 = 75 mm. Each crank adds 0.42 × 75 = 31.5 mm. A bar cranked at both ends adds 63 mm to its straight length, before hooks and bend deductions. If the cranks are cut at 30 degrees instead, the extra is 0.27D per crank.

How do you check a BBS on site?

You do not need to be an engineer to catch most BBS mistakes. Before the steel is cut, and again before the concrete goes in, check these:

• The bar count in the schedule matches the drawing for every member, and the spacing on site matches the count.
• The diameter on each bundle tag matches the bar mark. A 10 mm bar where a 12 mm was scheduled carries about 30% less steel.
• Cover is held by cover blocks of the right size, 50 mm under footings and 40 mm round column bars as IS 456 asks.
• Laps in neighbouring bars are staggered, not all at one level. IS 456 counts laps as staggered only when their centres are at least 1.3 times the lap length apart.
• Stirrup hooks are turned to 135 degrees and point into the core of the beam or column.
• The bar grade on the steel tags matches the grade the schedule was worked out for. Fe 500 laps are longer than Fe 415 laps, as the table above shows.

The total weight at the foot of the schedule is what goes into the steel order and the construction estimate. A little extra is always bought for offcuts and laps the drawing did not show. If the weight on the bill is far above the schedule total, ask for the cutting list that produced it. Choosing the steel itself, grade by grade, is covered in the guide to TMT bars.

Where the BBS fits in a house budget

Steel is the one material in a house you should take off a schedule rather than a thumb rule, and the BBS is that schedule. The plinth beam, columns, beams and slabs each get their own sheet. The plinth beam cost guide shows how one member’s steel, concrete and shuttering are priced from quantities like these. The shuttering rate guide covers the formwork that holds the steel in place for the pour. The house construction cost calculator puts the steel total next to every other block of the budget.

Once the steel is fixed and checked, the concrete has to be mixed to the grade the laps were worked out for. Compare live concrete mixer models and connect with a dealer for the pour. More estimating guides sit under construction cost.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication.

Code references: IS 2502 : 1963 (bending and fixing of bars for concrete reinforcement), Table I, Table II and clauses 3.2.1, 3.3, 5.1.1 and 9.1.2; IS 456 : 2000 (plain and reinforced concrete), clauses 26.2.1, 26.2.1.1, 26.2.2.1, 26.2.2.4, 26.2.5.1, 26.4.1 and 26.4.2; SP 34 : 1987 (handbook on concrete reinforcement and detailing), Table 4.1, the development length tables of Section 4, and Section 5. Development lengths are calculated for a bar stress of 0.87 fy. Bar weights are at d² ÷ 162 kg per metre. The worked examples are illustrations, not designs; your structural engineer’s drawing and schedule decide every bar.