- Select your unit system and geometry type.
- Enter span count, skew angle, and both overhangs.
- Provide deck dimensions for your chosen geometry.
- Add deductions for openings or unsurfaced zones.
- Optional: enter thickness, density, and rebar rate.
- Press Calculate. Download CSV or PDF if needed.
| Case | Geometry | Inputs | Net Area | Wearing Volume |
|---|---|---|---|---|
| A | Rectangular |
Metric; L=30 m; W=12 m; Skew=15°; Overhangs=0.5 m each; Deductions=6 m²; Thickness=60 mm |
≈ 406.062 m² | ≈ 24.364 m³ |
| B | Trapezoidal |
Metric; L=40 m; Wstart=10 m; Wend=14 m; Skew=10°; Overhangs=0.4 m each; Deductions=10 m²; Thickness=50 mm |
≈ 490.550 m² | ≈ 24.528 m³ |
| C | Multi‑segment |
Metric; Segments: (12 m×11 m), (18 m×12.5 m), (10 m×13 m); Skew=0°; Overhangs=0.3 m each; Deductions=8 m²; Thickness=45 mm |
≈ 520.300 m² | ≈ 23.414 m³ |
Why deck area matters in planning
Bridge deck area is a primary quantity for early cost, schedule, and material forecasting. Accurate plan area supports surfacing tonnage, waterproofing coverage, formwork planning, and traffic staging. It also informs curing time, lane closure durations, and crew loading. Small errors multiply when spans repeat and when widening details are overlooked during preliminary takeoff. For rehabilitation, area helps size milling, membrane removal, and deck protection zones, enabling consistent bid comparisons across alternatives through each project development phase.
Geometry selection for real bridges
Rectangular geometry fits straight, constant-width decks and is ideal for simple spans and uniform cross sections. Trapezoidal geometry represents tapers caused by approach flares or lane transitions, using average width along the effective length. Multi‑segment inputs suit stationed designs where width changes gradually with curb lines, parapets, and ramps, and where alignment shifts create localized widening.
Skew, overhangs, and deductions
Skewed abutments increase plan area because the effective deck length grows as ends rotate relative to the centerline. This calculator applies a cosine adjustment to approximate that increase for practical estimating. Overhangs capture sidewalks, barriers, and cantilevers beyond the nominal roadway width. Deductions remove scuppers, utility openings, joints, and zones not receiving surfacing or waterproofing layers.
Material quantities from net area
Once net area is known, wearing volume follows directly from thickness. Adding density converts volume to mass for procurement, plant scheduling, and hauling logistics. A mass‑per‑area allowance can approximate reinforcing steel for quick comparisons between concepts. Use the estimate to screen alternatives, then refine with bar schedules, lap allowances, and waste factors as design advances.
Quality checks and reporting outputs
Confirm dimensions match plan notes and station limits, and keep units consistent before calculating. Compare net area against a manual spot check from typical cross sections and a few stations. Review skew assumptions for very large angles and complex curvature. Use the CSV export for estimating sheets and the PDF export for submittals, assumptions, and internal reviews, and improves traceability of assumptions.
1) What deck width should I enter?
Enter the structural or surfaced width along the plan, then add overhangs using the left and right fields. This avoids double counting sidewalks, barriers, or cantilevers included outside the nominal roadway.
2) How does skew affect the area?
Skew increases plan area because the deck length projected on the centerline is shorter than the skewed end-to-end distance. The calculator approximates this using length divided by cosine of the skew angle.
3) When should I use the trapezoidal option?
Use trapezoidal geometry when the deck width transitions from one end to the other, such as approach flares or lane drops. The area is computed with the average of the start and end widths.
4) What belongs in deductions?
Include openings or zones that will not receive deck surfacing or waterproofing, such as large scuppers, utility pits, access hatches, or permanently unpaved areas. Keep deductions in the same area units.
5) Are material outputs suitable for final design?
They are planning quantities for estimating and comparison. Final quantities should come from detailed design drawings, specifications, and bar schedules, with appropriate waste, laps, and construction factors.
6) Why is my net area zero?
Net area is limited to a minimum of zero. If deductions exceed the computed gross area, reduce deductions or verify geometry, units, and span count. Recheck that lengths and widths are positive.