Guide
How to Choose a Steel Grating Specification
By DONGFU GRATING Engineering Team · Published 2026-06-24 · Updated 2026-07-17
Choosing a steel grating specification is a sequence of decisions taken in order. Start with the application and environment — platform, walkway, stair tread, trench cover, indoor, outdoor or corrosive — because they pre-select material and finish. Next fix the support span, measured in the bearing bar direction, and the load type: pedestrian traffic, uniform equipment loads, forklifts or trucks, with wheel loads needing contact-area data. Span and load together determine the bearing bar depth and thickness. Then choose material (carbon steel, stainless 304/316L or aluminum), surface type (plain or serrated) and finish (hot-dip galvanized, painted or mill). Set bearing bar and cross bar spacing for safety and drainage, and record panel sizes with the span direction marked, plus banding, cut-outs and fixing accessories. A complete specification such as G325/30/100 or 19-W-4 lets a supplier quote accurately without assumptions.
Step 1: Define the application and environment
Every specification decision starts from where the grating will work. An industrial platform, a public walkway, a stair tread, a trench cover and a marine catwalk all carry different safety expectations, drainage needs and corrosion exposure. State the application and whether the site is indoor, outdoor, wet, oily, chemical or marine — these two facts pre-select the material and finish before any dimension is discussed.
Step 2: Fix the support span and load
Span is the clear distance between supports, measured along the bearing bars — the bars must run in the support span direction. Define what the grating carries: pedestrian traffic, uniform equipment loads, forklifts or trucks. Vehicle loads need wheel load values and tire contact areas, not just gross vehicle weight.
Span and load together fix the bearing bar depth and thickness. Deeper, thicker bars carry more over longer spans; the final section is confirmed by the supplier against deflection limits and the safety factor your project requires.
- Pedestrian platforms and walkways: commonly designed around 3–5 kN/m²
- Uniform equipment loads: state kN/m² plus any concentrated point loads
- Forklifts and trucks: wheel load, tire contact area and traffic frequency
Step 3: Choose the material
| Material | Strengths | Limitations | Typical uses |
|---|---|---|---|
| Carbon steel Q235 (≈ A36 / S235JR) | Economical, strong, easy to weld | Needs corrosion protection outdoors | Most industrial platforms, walkways, treads, trench covers |
| Carbon steel Q355 (≈ A572 Gr.50) | Higher strength for long spans and heavy loads | Higher material cost | Large spans, docks, airports, truck areas |
| Stainless 304 / 304L | Corrosion resistant, hygienic | Higher material and fabrication cost | Food, pharmaceutical, brewery, general corrosive areas |
| Stainless 316 / 316L | Resists chlorides and salt spray | Highest material cost | Marine, offshore, chemical, wastewater |
| Aluminum 6061 / 6063 | One-third the weight of steel, corrosion resistant, non-sparking | Lower load capacity at equal size | Architectural, marine walkways, lightweight covers |
Step 4: Select surface type and finish
- Surface type: plain for dry, clean interiors; serrated for wet, oily, snowy, outdoor or sloped areas
- Finish on carbon steel: hot-dip galvanized after fabrication for outdoor and humid sites; painted or powder coated for color coding; mill finish only for indoor use or customer post-processing
- Stainless finishes: mill, passivated, abrasive blasted or electro-polished for hygiene and appearance
- Aluminum finishes: mill, clear or black anodized, or powder coated
Step 5: Set spacing and panel layout
Bearing bar spacing balances load capacity, opening safety and material use: 30 mm is the industrial default, 40 mm is more economical for moderate loads, and closer spacings suit public access. Cross bar spacing is typically 100 mm, with 50 mm where small-object protection or extra lateral stability matters. Record every panel as length × width with the span direction marked, and list cut-outs, banding, toe plates and fixing clips from the layout drawing.
How to read a grating specification code
Two naming systems are in daily use. The metric code combines bearing bar size with bar and cross bar pitch; the NAAMM imperial code combines a spacing series, a construction letter and a cross bar spacing in inches. Both describe the same physical grid.
| Code element | Meaning | Notes |
|---|---|---|
| G325/30/100 (metric) | Bearing bar 32 × 5 mm, 30 mm bearing bar pitch, 100 mm cross bar pitch | G = grating; 325 encodes 32 × 5 mm |
| G253/30/50 (metric) | Bearing bar 25 × 3 mm, 30 mm pitch, 50 mm cross bar pitch | Common light-platform specification |
| 19-W-4 (NAAMM) | Bearing bars ≈ 1-3/16 in on center, welded, cross bars at 4 in | The imperial default, ≈ 30 × 100 mm |
| 15-W-2 (NAAMM) | Bearing bars ≈ 15/16 in on center, welded, cross bars at 2 in | Closer mesh for public areas |
| Construction letters | W = welded, SL = swage locked, DT = dovetail pressure locked | Defines how bars are joined |
Write the complete specification line
A ready-to-quote line reads: welded steel grating, Q235 carbon steel, bearing bar 32 × 5 mm, spacing 30 × 100 mm, serrated surface, hot-dip galvanized per ASTM A123, panels 1000 × 6000 mm with span along the 1000 mm direction, banded ends, saddle clips. Add drawings where the layout has cut-outs or irregular shapes, and state quantity in pieces, square meters or tons.
If any element is unknown, say so — our engineers can propose a specification from application, span, load and environment before pricing. Work through the quotation checklist to make sure nothing is missing, then send it via the inquiry form on the contact page.
Common Mistakes to Avoid
- Confusing span direction with panel width — bearing bars must run in the support span direction; reversing them is a structural failure, not a detail
- Choosing bar size by habit or by what a previous project used, instead of confirming span and load
- Asking for a price per square meter without load, span or finish — any answer is a guess
- Choosing plain surface for oily or outdoor walkways to save cost, then retrofitting anti-slip measures
- Forgetting banding and cut-out details until fabrication has started
Quick Checklist
- Application and environment stated
- Support span measured in the bearing bar direction
- Load type defined (pedestrian / uniform / wheel load with contact area)
- Material selected (or "unknown — advise me")
- Plain or serrated surface decided
- Finish selected
- Bearing bar and cross bar spacing chosen
- Panel sizes listed with span direction marked
- Banding, cut-outs, toe plates and clips noted
- Quantity stated with units