Rebar Quantity Take-Off Method — How to Calculate Steel Weight for Your Order

What Is a Rebar Quantity Take-Off?

A rebar quantity take-off is the process of extracting every reinforcing bar from a set of structural drawings, calculating its linear length, applying the weight-per-metre formula for that diameter, and summing the result into a schedule of tonnes by bar diameter. The output feeds directly into procurement — it is the document you send to your supplier when requesting a quote, and it becomes the basis of your purchase order.

An accurate QTO prevents two common problems: over-ordering (tying up cash and storage space at the destination) and under-ordering (causing construction delays while you wait for supplementary shipments). For export orders crossing international borders, the QTO also informs container loading calculations and freight cost estimates.

The Rebar Weight Formula

The standard weight formula for steel rebar is derived from the density of steel (7,850 kg/m³) and the cross-sectional area of a circular bar:

Weight (kg/m) = d² (mm) × 0.00617

Where d is the nominal diameter in millimetres. This formula is exact for the standard steel density and gives results consistent with DIN 488 nominal weight values. For example:

• 12 mm bar: 12² × 0.00617 = 144 × 0.00617 = 0.888 kg/m
• 16 mm bar: 16² × 0.00617 = 256 × 0.00617 = 1.578 kg/m
• 20 mm bar: 20² × 0.00617 = 400 × 0.00617 = 2.468 kg/m

Step-by-Step Rebar QTO Method

Follow these five steps to produce a complete take-off schedule from structural drawings:

Step 1 — Gather drawings and bar bending schedules

Collect all structural layout drawings and, if available, the bar bending schedule (BBS) prepared by the structural engineer. A BBS lists every bar by its shape code (DIN 488 or BS 8666 shape codes), diameter, total length per bar, and number of bars. If a BBS is not available, you will need to measure lengths directly from the reinforcement layout drawings.

Step 2 — List every unique bar by diameter

Create a spreadsheet with columns: bar mark, diameter (mm), shape code, total cut length per bar (m), quantity (No.), and total linear metres. Group bars by diameter. Include lap lengths — for B500B, standard lap lengths per Eurocode 2 range from approximately 40–60× the bar diameter depending on cover and concrete class.

Step 3 — Calculate total linear metres per diameter

Multiply the cut length per bar by the quantity for each bar mark. Sum to get total linear metres per diameter across the entire structure.

Step 4 — Convert to kilograms and tonnes

Apply the weight formula: total metres × weight kg/m for that diameter. Sum all diameters to get the overall tonnage. Add a wastage allowance (typically 3–5% for cut-and-waste on complex shapes) if the BBS does not already account for it.

Step 5 — Format the procurement schedule

Present your take-off as a table showing diameter, total kg, and total tonnes. Include the required grade (B500B or B500C), delivery standard (DIN 488 / EN 10080), required lengths, and destination port. This is the information your supplier needs to provide an accurate quotation. See the rebar procurement checklist → for the full set of details to include.

Worked Example — Simple Raft Foundation

Consider a 20 m × 15 m raft slab reinforced with T16 bars at 200 mm centres both ways, top and bottom (4 layers). Indicative calculation:

• Bars in one direction: 20 m span ÷ 0.2 m spacing = 100 bars per layer; 4 layers × 2 directions = 800 bar runs
• Bar length per run ≈ 15 m (plus laps on longer spans — simplified here)
• Total linear metres T16: 800 × 15 = 12,000 m
• Weight at 1.58 kg/m: 12,000 × 1.58 = 18,960 kg ≈ 19.0 tonnes

This is a simplified indicative calculation for illustration. A real project BBS would account for varying bar lengths, laps, hooks, and trimmer bars, and the structural engineer’s drawings take precedence. Always have your QTO reviewed against the structural design before placing an order.