Rebar calculator for beams & stirrups
Enter the beam size, cover, longitudinal bars and stirrup spacing. You get stirrup count and cut length, bar lengths with laps and hooks, and the weight by bar size, ready for a takeoff sheet.
- Top and bottom bars
- Stirrup count and length
- Laps and hooks
- Weight by bar size
1 · Beam
2 · Longitudinal bars
3 · Stirrups
4 · Order
Bar weights, diameters and areas: ASTM A615/A615M standard inch-pound bar sizes (also in the CRSI Manual of Standard Practice). Stirrup hook default: 135° hook extension of 6 db, not less than 3 in, per ACI 318 standard hook geometry for stirrups and ties; your detail governs. Cover, first-stirrup offset and laps are editable.
Weight by bar group
Live formula
Save your results
Copy these results, then add your approved sample files in the trial brief.
A simply reinforced rectangular beam
The calculator handles the common case: a rectangular beam with straight top and bottom bars and closed stirrups at a uniform spacing. Each input mirrors a line on a typical beam schedule: mark, size, top bars, bottom bars, stirrup size and spacing. Where the schedule calls for different spacing near the supports than at midspan, run the beam as two segments.
- Longitudinal bars. Beam length minus end cover, plus a lap or hook allowance per bar from the detail. Continuous top bars over supports and bottom bars that extend into columns are common reasons the allowance is not zero.
- Stirrups. Count = (length − 2 × first stirrup offset) ÷ spacing + 1. ACI detailing typically places the first stirrup within 2 in of the support face; check the schedule.
- Stirrup length. The perimeter of the stirrup inside the cover, plus the hook extensions at the closure.
- Weight. Linear feet by bar size times the ASTM A615 nominal weight.
Bars, stirrups and weight
| Bar | lb/ft | Typical use in beams |
|---|---|---|
| #3 | 0.376 | Stirrups, ties |
| #4 | 0.668 | Stirrups, light top bars |
| #5 | 1.043 | Top bars |
| #6 | 1.502 | Bottom bars |
| #8 | 2.670 | Heavier bottom bars |
Typical uses are general patterns only; the structural drawings govern every bar.
Building the beam takeoff
On a cast-in-place job, beams are where rebar takeoffs bog down: dozens of marks, each with spans, bars that run continuous over several supports, and stirrup zones. A good takeoff sheet keeps one row per mark and span with the source sheet noted, so a change in an addendum can be traced to the rows it affects. The calculator gives you a quick, checkable number for one mark; your spreadsheet or detailing software carries the rest.
RenderDraw's AI takeoff reads beam schedules and framing plans together, proposes marks, spans and counts with links to the sheet, and leaves unresolved items open for an estimator. You stay in control of the detailing assumptions; the software takes on the search-and-count work.
Rebar and concrete quantities you can trace back to the sheet.
RenderDraw's AI takeoff proposes counts, lengths and areas from structural drawings and schedules, keeps the source on every row, and holds uncertain items for estimator review.
- Footing, slab and wall schedules read in context. Quantities stay linked to the schedule and plan that produced them.
- Review queue sorted by confidence. Work the questionable items first.
- Addenda through the same review. Send the changed sheets back through takeoff and estimator review.
- Estimator approval before pricing. Laps, waste, accessories and labor stay with you.
Send one structural set
Include the foundation plan and schedules. Files stay private while RenderDraw assesses the request. No obligation.
RenderDraw does not publish accuracy percentages or time-saved claims. Test it on your own plan set.
Questions estimators ask.
How do you calculate the number of stirrups in a beam?
Subtract the first-stirrup offset at each end from the beam length, divide by the spacing, round down, and add one. For 20 ft with 8 in spacing and 2 in offsets, that is floor((240 − 4) ÷ 8) + 1 = 30 stirrups.
How do you calculate stirrup cut length?
Add the four sides of the stirrup inside the cover, then add hook extensions at the closure. A 12 × 24 in beam with 1.5 in cover has a stirrup perimeter of 2 × 9 + 2 × 21 = 60 in before hooks.
How much does #6 rebar weigh?
1.502 lb/ft per ASTM A615.
Does this include lap splices?
Enter a lap or hook allowance per bar. Lap lengths depend on bar size, concrete strength, cover and spacing per ACI 318, so take them from the drawings or the detailer.
Can RenderDraw read beam schedules?
RenderDraw's AI takeoff reads schedules and plans and proposes quantities with their sources for estimator review. Request a free sample takeoff.
Beam schedules are where rebar takeoffs slow down.
Send a structural set. RenderDraw proposes beam marks, sizes and lengths from plans and schedules with their source sheet, and flags anything it cannot tie together.
- Upload the plans, specs and schedules, plus an addendum if you have one.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with extracted quantities, flagged items and next steps.