| Deck (L×W) | Cover | Top Mat | Bottom Mat | Lap | Waste | Typical Outcome |
|---|---|---|---|---|---|---|
| 30 m × 12 m | 50 mm | 16 mm @150/200 | 20 mm @150/200 | 0.60 m | 3% | Weight depends on selected directions. |
- Effective Length = Deck Length − 2 × Cover
- Effective Width = Deck Width − 2 × Cover
- Number of Bars = ⌊Effective Dimension / Spacing⌋ + 1
- Bar Length = Run Dimension + Lap/Allowance
- Unit Weight (kg/m) = d² / 162, where d is in mm
- Group Weight = Total Length × Unit Weight
- Total = Subtotal × (1 + Waste%/100)
- Enter the bridge deck length and width, then set cover.
- Set a lap/allowance per bar to cover splices and detailing.
- Select the mats you need: top, bottom, or both.
- Enable longitudinal and transverse directions as required.
- Choose bar diameters and spacings from your reinforcement drawings.
- Set a waste percentage for cutting, bends, and handling.
- Click calculate, then export CSV or PDF for documentation.
1) Why rebar weight matters in deck planning
Bridge deck reinforcement is often ordered by mass, not by count. A reliable weight estimate improves procurement, crane planning, storage, and cut-and-bend scheduling. For typical decks, small changes in spacing or bar size can shift totals by hundreds of kilograms, affecting cost and delivery timing.
2) How spacing drives total bar count
Bar quantity is governed by spacing across the effective dimension. The calculator uses ⌊effective / spacing⌋ + 1, which aligns with common detailing practice when bars start near an edge and continue at regular centers. For example, reducing spacing from 200 mm to 150 mm increases bar count by about 33%, and the associated weight rises in the same direction.
3) Bar diameter and unit mass relationship
Unit mass increases with the square of diameter. Using d²/162 (kg/m), a 16 mm bar is about 1.58 kg/m, while a 20 mm bar is about 2.47 kg/m. This means upgrading a mat from 16 mm to 20 mm can increase weight by roughly 56%, even before spacing changes are considered.
4) Cover, laps, and detailing allowances
Cover reduces the effective length and width, so it lowers bar run length and count slightly. Laps and allowances add length to every bar, so they can noticeably increase totals on large mats. If lap is 0.60 m and you have 400 bars, that alone adds 240 m of steel length. Adjust this value to reflect splices, hooks, and anchorage requirements.
5) Waste factors and reporting for approvals
Waste allowances commonly range from 2% to 7% depending on bar complexity and site handling. Use higher values when there are many cut lengths, congested reinforcement zones, or frequent changes. Exporting a breakdown by mat and direction supports internal checks, quantity tracking, and client documentation during inspections.
1) Does the calculator include both directions automatically?
No. You can enable longitudinal and transverse directions separately for each mat. This lets you match drawings that omit one direction or use different spacing patterns.
2) What does “lap/allowance per bar” represent?
It is extra length added to every bar to cover splices, laps, hooks, and anchorage. Increase it when detailing requires longer development or when bars are cut with added ends.
3) Why does bar diameter change weight so much?
Steel weight per meter increases with diameter squared. A small diameter upgrade can significantly raise total mass, especially on dense mats with many bars.
4) How is effective deck size calculated?
The calculator subtracts cover from both sides: effective length = deck length − 2×cover, and effective width = deck width − 2×cover. This represents the bar run inside cover limits.
5) Should I use meters or feet and inches?
Use whichever is convenient. Length and width can be entered in meters or feet, and spacing/cover/lap can be entered in millimeters, inches, or meters. Results are standardized internally.
6) What waste percentage is typical for bridge decks?
Many projects start with 3% to 5% for straight bar mats. Use 6% to 7% when there are many bends, varied cut lengths, tight reinforcement zones, or frequent revisions.
7) Can I use this for bundled bars or multiple layers?
Yes for multiple layers by treating each layer as a mat and entering its spacing and diameter. For bundled bars, calculate each bar separately and sum, or increase diameter inputs carefully to match the bundle mass.