A 250 x 355 mm RCC floor beam running across two bays of 3.5 m and 4.0 m (column centres) in a Nepali house needs about 0.39 m3 of M20 concrete below the slab, or a little over 3 bags of cement, and about 77 kg of Fe500 steel when it has 3 bars of 12 mm at the top, 3 bars of 12 mm at the bottom, 2 extra 12 mm top bars over each support and 8 mm stirrups. For a whole two storey house on a 3 x 4 column grid, the plinth beams and two floors of beams together come to about 11.5 m3 of concrete, 93 bags of cement and 1.8 tonnes of steel. This page shows how each of those numbers is worked out, so you can repeat it for your own drawing, check a contractor's bill, or answer beam quantity questions in the NEC licence and Lok Sewa exams.
The bar rules used here come from NBC 205:2024, Nepal's ready to use detailing guideline for RC framed houses up to three storeys, and from IS 456:2000. The numbers are a worked example. Your approved structural drawing always decides the final size, bars and spacing.
What NBC 205:2024 says about beams
Check your drawing against these points before you start counting. If the beam on your plan is very different, ask the designer why before you order steel.
- Plinth (tie) beam: 250 mm wide and 355 mm deep in both directions, sitting on a toe wall, with 3 bars of 12 mm at the top and 3 at the bottom running through the full length.
- Floor and roof beams: 250 mm or 300 mm wide and 355 mm or 380 mm deep for the first floor, and 250 x 355 mm for the upper floors and roof. The depth includes the slab thickness.
- Materials: M20 concrete (nominal mix 1 : 1.5 : 3) and Fe500 TMT bars for main bars and stirrups.
- Span: the tables cover beam spans up to 4.5 m, and bays between 2.1 m and 4.5 m.
- Main bars: for a two storey house the tables give 3-12 mm through bars at top and bottom. In the higher seismic zones, the first floor beams get 2 extra 12 mm bars at the top over each support. Extra bars stop at 0.3 times the span from the face of the support, and are not cut off at all where the span is less than 2.1 m.
- Stirrups: closed 8 mm stirrups with 135 degree hooks (hook extension at least 65 mm), at 100 mm near the supports and 150 mm in the middle part of the span.
- Cover: 25 mm clear cover to the stirrups in beams (columns use 40 mm, footings 50 mm at the bottom).
- Laps: at least 57 times the bar diameter, top bars lapped only in the middle third of the span, bottom bars only in the zones near the supports, and not more than half the bars lapped at one section.
IS 456 adds two checks that the NBC tables already satisfy for ordinary houses: the minimum tension steel is 0.85 bd / fy (clause 26.5.1.1), and the maximum is 4 percent of the gross section. For a 250 x 355 mm beam with an effective depth of about 316 mm, the minimum is 0.85 x 250 x 316 / 500 = 134 mm2. Three 12 mm bars give 339 mm2, so the 3-12 layout is well above the minimum.
How to measure beams without double counting
Most errors in beam estimates come from counting the same concrete twice. Use these rules and stay with them for the whole house:
- Length: take the clear span between column faces. The concrete at the beam-column joint is already in the column quantity.
- Depth of floor beams: take only the part below the slab. A 355 mm beam under a 125 mm slab is measured as 355 - 125 = 230 mm deep, because the slab is measured as a full panel over the beams.
- Plinth beams: there is no slab above them, so take the full 355 mm depth.
- Steel: take the full bar lengths, including the parts that go into the columns. Steel is not double counted the way concrete is, because column bars and beam bars are separate bars.
Worked example 1: one floor beam line over two bays
Take one line of first floor beam in a house with 350 x 350 mm columns (the column used in our RCC column quantity example). The data:
| Item | Value |
|---|---|
| Beam size | 250 x 355 mm overall, slab 125 mm |
| Column centres | 3.5 m and 4.0 m (two bays, three columns) |
| Clear spans | 3.5 - 0.35 = 3.15 m and 4.0 - 0.35 = 3.65 m |
| Main bars | 3-12 mm top and 3-12 mm bottom, through |
| Extra bars | 2-12 mm top over each support, to 0.3 L |
| Stirrups | 8 mm, 100 mm in 2d end zones, 150 mm in the middle |
| Cover | 25 mm to stirrups, 40 mm at the outer face of end columns |
Step 1: concrete
Total clear length = 3.15 + 3.65 = 6.80 m.
Volume below the slab = 6.80 x 0.25 x 0.23 = 0.391 m3. If you measured the full depth by mistake you would get 6.80 x 0.25 x 0.355 = 0.604 m3, more than half as much again.
Using a dry volume factor of 1.54 and M20 (1 : 1.5 : 3, total 5.5 parts), the same factors as our cement bags for 1 m3 of M20 post:
- Dry volume = 0.391 x 1.54 = 0.602 m3
- Cement = 0.602 x 1 / 5.5 x 1440 = 157.6 kg = 3.15 bags of 50 kg
- Sand = 0.602 x 1.5 / 5.5 = 0.164 m3
- Aggregate = 0.602 x 3 / 5.5 = 0.328 m3
Step 2: through bars
The outer length of the beam line, from the outer face of one end column to the other, is 3.5 + 4.0 + 0.35 = 7.85 m. Take off 40 mm cover at each end and add a 320 mm bend down into each end column (the anchorage allowance used in this example; use the value on your drawing):
Through bar length = 7.85 - 2 x 0.04 + 2 x 0.32 = 8.41 m. This is less than 12 m, so each bar is one piece with no lap.
Six through bars = 6 x 8.41 = 50.46 m. At 0.889 kg/m for 12 mm bars (d x d / 162, see the D2/162 formula), weight = 44.85 kg.
Step 3: extra top bars
- End support A: 0.3 x 3.15 + 0.35 - 0.04 + 0.32 = 1.575 m
- Middle support B: 0.3 x 3.15 + 0.35 + 0.3 x 3.65 = 2.390 m
- End support C: 0.3 x 3.65 + 0.35 - 0.04 + 0.32 = 1.725 m
Two bars at each support = 2 x (1.575 + 2.390 + 1.725) = 11.38 m, weight = 10.12 kg.
Step 4: stirrups
Effective depth d = 355 - 25 - 8 - 6 = 316 mm, so each end zone is 2d = 632 mm. Stirrup size inside the cover = 200 x 305 mm. With a 10d hook allowance and the usual bend deductions (3 bends of 90 degrees at 2d and 2 bends of 135 degrees at 3d), the cutting length is 2 x (200 + 305) + 160 - 48 - 48 = 1,074 mm. Our bar bending schedule for beams post explains this formula in detail.
- Each end zone, first stirrup 50 mm from the column face: (632 - 50) / 100 = 5.8, so 5 spaces + 1 = 6 stirrups
- Bay 1 middle zone: 3,150 - 2 x 632 = 1,886 mm at 150 mm = 12 stirrups. Bay 1 total = 6 + 6 + 12 = 24
- Bay 2 middle zone: 3,650 - 2 x 632 = 2,386 mm at 150 mm = 15 stirrups. Bay 2 total = 6 + 6 + 15 = 27
51 stirrups x 1.074 m = 54.77 m of 8 mm bar at 0.395 kg/m = 21.64 kg.
Result for example 1
| Item | Length (m) | Weight (kg) |
|---|---|---|
| Through bars 6-12 mm | 50.46 | 44.85 |
| Extra top bars 12 mm | 11.38 | 10.12 |
| Stirrups 8 mm (51 nos) | 54.77 | 21.64 |
| Total steel | 76.61 | |
| Concrete below slab | 0.391 m3 (3.15 bags of cement) | |
| Shuttering (bottom + two sides below slab) | 6.80 x (0.25 + 2 x 0.23) = 4.83 m2 | |
That is about 11.3 kg of steel per running metre of beam. You can check the bar weights with our steel weight calculator and the concrete with the concrete calculator.
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Worked example 2: all beams of a two storey house
Now apply the same method to every beam of a house with 12 columns on a 3 x 4 grid. Bays in the X direction are 3.5 m and 4.0 m; bays in the Y direction are 3.0 m, 3.6 m and 4.2 m. There are 4 beam lines in X (two bays each) and 3 beam lines in Y (three bays each), at plinth level, first floor and roof.
- Clear length of one X line = 3.15 + 3.65 = 6.80 m; 4 lines = 27.20 m
- Clear length of one Y line = 2.65 + 3.25 + 3.85 = 9.75 m; 3 lines = 29.25 m
- Total clear beam length per level = 56.45 m
The Y lines are 3.0 + 3.6 + 4.2 + 0.35 = 11.15 m long outside to outside, so their through bars come to 11.15 - 0.08 + 0.64 = 11.71 m. That still fits in one 12 m bar, with only 0.29 m of off-cut.
| Level | Concrete (m3) | Cement (bags) | 12 mm steel (kg) | 8 mm steel (kg) | Shuttering (m2) |
|---|---|---|---|---|---|
| Plinth beam, 250 x 355 full depth | 5.01 | 40.4 | 366.8 | 182.0 | 40.08 (sides only) |
| First floor beams, 230 mm below slab | 3.25 | 26.2 | 448.9 | 182.0 | 40.08 |
| Roof beams, 230 mm below slab | 3.25 | 26.2 | 448.9 | 182.0 | 40.08 |
| Total | 11.50 | 92.8 | 1,264.6 | 546.0 | 120.24 |
Total steel for all beams = 1,810.6 kg, about 1.8 tonnes. Sand comes to 4.83 m3 and aggregate to 9.66 m3. The plinth beam has no extra bars, which is why its 12 mm steel is lower. In this example the roof beams use the same bars as the first floor to keep the sums simple; in many drawings the roof beams in low seismic zones have no extra bars, so read your own table. The plinth beam shuttering is counted on the two sides only, because the beam sits on the toe wall and soling.
Add about 3 to 5 percent to the steel for off-cuts and wastage when you order, and round cement up to whole bags. Do not add wastage to the quantity in the measurement book; that is for ordering only.
Quick tables for other beam sizes
Concrete and cement per running metre
| Beam (mm) | Full depth (m3/m) | Bags/m full | Below 125 mm slab (m3/m) | Bags/m below slab |
|---|---|---|---|---|
| 230 x 355 | 0.0817 | 0.66 | 0.0529 | 0.43 |
| 250 x 355 | 0.0888 | 0.72 | 0.0575 | 0.46 |
| 250 x 380 | 0.0950 | 0.77 | 0.0638 | 0.51 |
| 300 x 380 | 0.1140 | 0.92 | 0.0765 | 0.62 |
Steel per running metre
| Item | kg per metre of beam |
|---|---|
| 3-12 top + 3-12 bottom | 5.33 |
| 4-12 top + 4-12 bottom | 7.11 |
| 3-16 top + 3-12 bottom | 7.41 |
| 8 mm stirrups at 150, 250 x 355 beam | 2.83 |
| 8 mm stirrups at 100, 250 x 355 beam | 4.24 |
| 8 mm stirrups at 150, 300 x 380 beam | 3.22 |
A quick check: a 250 x 355 mm beam with 3-12 top and bottom and mixed stirrup spacing usually lands between 9 and 12 kg per metre, before extra bars. If a bill shows 20 kg per metre for the same beam, ask for the bar bending schedule.
Step-by-step method for your own house
- Mark every beam line on the structural plan for each level: plinth, each floor, roof. Note the beam size and the bar table used.
- Work out the clear spans between column faces for each line.
- Find the concrete: clear length x width x depth (below slab for floor beams, full depth for plinth beams).
- Find the through bar length for each line: outer length minus end cover plus the anchorage bend at each end column. If it is over 12 m, add one lap of 57 d per bar per joint and place it in the allowed zone.
- Add the extra bars at each support: 0.3 L into each side, plus the column width, plus the bend at end columns.
- Count stirrups in each zone of each bay and multiply by the cutting length.
- Multiply each length by d x d / 162 to get kg, then add up by diameter. Steel is bought by diameter, so keep 8, 10, 12 and 16 mm totals separate.
- Convert concrete to cement bags, sand and aggregate, and add shuttering area for the formwork contractor.
Common mistakes seen on Nepali sites
- Measuring floor beams to the full depth. This double counts the slab part and can add 50 percent to beam concrete.
- Using centre to centre length for concrete. The joint concrete then appears in both the column and the beam.
- Bending the stirrup hooks at 90 degrees. NBC 205 asks for 135 degree hooks. A 90 degree hook opens up in an earthquake, which is one of the failures seen in 2015.
- Same stirrup spacing all along the beam. Masons often space all stirrups at 150 or even 200 mm. The end zones near the columns must be at 100 mm.
- Lapping top bars over the support. Top bars carry the most tension near the columns. Laps belong in the middle third for top bars.
- Too little cover. Stirrups touching the formwork mean rust stains within a few years. Use 25 mm concrete cover blocks under the bottom bars and on the sides.
- Ignoring off-cuts. A 12 m bar cut to 8.41 m leaves 3.59 m. Plan the BBS so off-cuts become extra bars or stirrups, instead of scrap.
Frequently asked questions
What is the standard beam size for a house in Nepal?
Under NBC 205:2024, 250 x 355 mm (including the slab) is the usual size for floor and roof beams of houses up to three storeys, with 250 x 380 or 300 x 380 mm allowed for the first floor. The plinth beam is 250 x 355 mm. The old 230 x 230 mm "tie beam" is not part of the guideline.
How much steel is needed per cubic metre of beam?
In example 1 it is 76.6 kg for 0.604 m3 of full section, or about 127 kg per m3. Expressed against concrete below the slab only, the figure looks much higher, which is why per-metre figures are easier to compare for beams.
How long should the beam props stay?
IS 456 gives 14 days for props under beams up to 6 m span, with longer times for larger spans. Many sites in Nepal remove props too early to reuse them on the next floor; avoid this.
Do these rules apply to a three storey house?
NBC 205:2024 has separate tables for three storey buildings, with heavier bars in the lower floors. The method on this page is the same; only the bar numbers change.
Related tools and practice
This post completes our house quantity series with the isolated footing, RCC column and RCC slab examples. Try the free engineering tools for quick checks, and practise estimating questions on the engineering MCQ practice page before the licence exam.
Sources
- NBC 205:2024 detailing guideline for RC buildings up to three storeys (PDF hosted by Birendranagar Municipality): clause 7.4 member sizes, section 8.3 beam tables and notes
- IS 456:2000 Plain and Reinforced Concrete: clauses 26.5.1 (beam steel limits) and 11.3 (stripping time of formwork)
- Department of Urban Development and Building Construction (DUDBC)
Seismic zone, soil type and the bar tables differ between sites, and municipalities may ask for a designed drawing instead of the guideline. Confirm the final details with your designer and your municipality's building section.
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