Calculator Inputs
Example Data Table
| Scenario | Girders | Length (m) | Height (mm) | Pitch (mm) | Top/Bottom/Web (mm) | Waste (%) |
|---|---|---|---|---|---|---|
| Typical slab reinforcement girder batch | 10 | 6.00 | 150 | 200 | 10 / 8 / 6 | 3.0 |
| Short girder for opening trimming | 24 | 2.40 | 120 | 150 | 8 / 8 / 5 | 4.0 |
| Heavier girder with tighter web spacing | 6 | 9.50 | 200 | 150 | 12 / 10 / 7 | 5.0 |
Tip: use your project drawing details for height, pitch, and bar sizes.
Formula Used
How to Use This Calculator
- Enter the number of girders and the girder length from drawings.
- Set girder height and web pitch to match the fabrication pattern.
- Select bar diameters for top chord, bottom chord, and web bars.
- Add end allowance and waste percentage if required by your shop method.
- Press Calculate to view totals above the form.
- Use Download CSV or Download PDF for reports.
Lattice Girder Quantity Planning Guide
Lattice girders are commonly used to stabilize reinforcement cages, support fresh concrete during placement, and maintain cover in slab and deck systems. Accurate quantity take-off improves procurement, reduces cutting loss, and helps fabricators standardize shop lengths. This calculator estimates chord and web steel based on a clear geometric model, then converts total lengths into weight using a practical unit-weight relation for bar diameters.
Start with the drawing or shop schedule. The girder length is the overall span of each unit, while the height is the vertical distance between top and bottom chords. Web pitch controls how frequently the diagonal web repeats; tighter pitch increases web length and weight, but can improve stiffness and handling. End allowance is optional and should reflect your anchorage, hooks, or trimming practice. If your shop uses laps, bundling, or conservative cutting plans, apply a waste percentage that matches real site experience.
The outputs are organized for fast checking. Panels per girder are calculated using ceil(L/p), which avoids under-counting when length is not an exact multiple of pitch. The diagonal length uses the Pythagorean relationship, so both pitch and height directly influence web steel. If your detail shows a doubled zig-zag (two diagonals per panel), enable the double web option to scale web bar count and length accordingly.
Example application: For a typical batch of 10 girders at 6.0 m length, 150 mm height, and 200 mm pitch, with top/bottom/web bars 10/8/6 mm and 3% waste, you will see chord lengths close to the batch length plus allowances and a web quantity driven by the number of panels. Use the table above to compare alternative scenarios, such as tightening pitch to 150 mm or increasing chord diameters for heavier loads.
For professional reporting, export to CSV for quick sharing with estimators or planners, and export to PDF for submittals and internal approvals. Before final purchase, reconcile these quantities with bar stock lengths, bending schedules, and any project-specific detailing rules. Minor detailing changes (laps, hooks, splices, and end treatments) can materially affect total weight, so use the waste factor and allowance fields to align the estimate with your fabrication method.
Detailing varies, so use allowance and waste to reflect laps, hooks, bends, and trimming. For tenders, compare a typical waste value with a conservative one.
- Use measured pitch from the detail, not a nominal spacing.
- Increase waste when using short stock lengths or many cut pieces.
- Validate one girder manually, then scale up with confidence.
FAQs
1) What does “web pitch” mean in this calculator?
Web pitch is the horizontal spacing between repeating web panels along the girder. A smaller pitch increases panel count and total diagonal length, raising web steel weight.
2) How is the diagonal web bar length calculated?
Diagonal length is calculated from pitch and height using √(p² + H²). This approximates each diagonal as a straight bar between chords.
3) Why does the calculator use ceiling for panels?
Ceiling ensures a partial last panel is still counted. It prevents underestimating web quantity when the girder length is not a perfect multiple of pitch.
4) What is “end allowance” and when should I add it?
End allowance adds extra length to each chord end for anchorage, bends, trimming, or fabrication practice. Use it when your shop detail extends chords beyond the clear span.
5) Does the weight formula match standard rebar tables?
It uses the common approximation kg/m = 0.006165 × d² (d in mm). Minor differences can occur versus specific national standards, but it is suitable for estimating.
6) When should I enable the double web option?
Enable it when your girder detail shows two diagonals per panel or a doubled zig-zag pattern. The calculator will multiply web count and length accordingly.
7) How should I choose a waste percentage?
Use your historical cutting loss and detailing practices. Typical ranges are 2–5% for organized fabrication and higher when stock lengths are limited, laps are frequent, or handling losses occur.