Steel / Rebar Weight Calculator

Steel reinforcement is priced almost entirely by weight, so the estimating question is always the same: how many tonnes of rebar does this element take? The answer comes from a single load-bearing formula — the diameter squared over 162 for kilograms per metre — applied to the total length of bar you plan, which for a slab means counting bars in both directions at the spacing, then adding laps and waste.

Steel / Rebar Weight Calculator takes either a simple run of bars (size × length × count) or a full slab grid (length, width, spacing) and returns the unit weight, total length, kilograms, pounds and metric tonnes, plus the bar counts. Choose metric or imperial and any standard size from 6 mm to 40 mm.

Underneath is a guide to standard bar sizes and their weights, the laps and cover rules that affect the count, and how to read a reinforcement schedule. Everything runs in your browser; nothing is uploaded.

• Two estimating modes: A simple bar run (size, length, count) or a full slab grid with spacing in both directions.
• All standard sizes: 6 to 40 mm metric bars plus a custom diameter, and imperial notes in the guide.
• d²/162 unit weight: The standard kilograms-per-metre formula built in and shown transparently.
• Metric or imperial: Lengths in metres or feet; results in kg, tonnes and pounds.
• Slab grid solver: Counts bars along length and width automatically from the c/c spacing.
• Laps & waste: An adjustable allowance (default 12%) to cover laps, cut-offs and site waste.
• Full tonnage: Total weight in metric tonnes for ordering, haulage and cost allocation.
• Reports & export: Copy or download the estimate as text, CSV or JSON.
• Learning guide: Bar size/weight table, laps, cover and reading the schedule built into the tool.

1. Pick the mode. Bar run for a set of identical bars, or slab grid to count bars across a floor slab.
2. Set the unit. Metres or feet for all lengths; the weight reports both metric and imperial.
3. Choose the bar diameter. Select from 6–40 mm or enter a custom size.
4. Enter the runs. Bar length and count, or the slab length, width and c/c spacing.
5. Set the laps & waste. 12% is a reasonable default for laps and wastage.
6. Read the weight. Unit weight, total length, kg, lb and tonnes appear instantly.
7. Export the bill. Copy or download the estimate as text, CSV or JSON for site ordering.

Example 1 — Column bars. 6 bars of 16 mm at 3.5 m each: 1.58 kg/m × 21 m = 33.2 kg. Around 6% of that again goes to laps in the lap zone.

Example 2 — Beam run. 4 bars of 20 mm over 6 m: 2.466 kg/m × 24 m = 59.2 kg, plus anchorage and bends, so allow about 10% extra.

Example 3 — Slab grid. A 5 × 4 m slab with 12 mm bars at 200 mm both ways: 21 + 26 bars ≈ 47 bars and about 200 m, weighing roughly 178 kg before laps.

Example 4 — Ordering in tonnes. 12 mm rebar at 0.888 kg/m over 2000 m is 1.78 tonnes — order 2.0 tonnes to cover laps and haulage breaks.

Example 5 — Checking a schedule. A bent-up bar schedule lists 10 bars of 16 mm at 6.1 m. The calculator gives 96.4 kg; the quantity surveyor adds laps and chairs to match the real purchase order.

• Weigh the whole job: From a bare run or a slab grid, in kilograms, pounds and tonnes at once.
• Fast grid counts: No manual adding — bars in each direction drop out of the length, width and spacing.
• Standard sizes covered: Every common metric diameter with a custom option for anything else.
• Order the steel: The tonnage figure lines up with how rebar is sold, priced and hauled.
• Verify any quote: Cross-check a contractor schedule against the d²/162 unit weights.
• Plan wraps and laps: The laps & waste field builds realistic site allowances in.
• Export the bill: Text, CSV and JSON summaries drop straight into material schedules.
• Free and private: No account, no watermark, nothing uploaded.