Technical and procurement guide · 10 August 2026
G60 vs G90 Galvanized Steel Coil: Coating Designations Explained
Read continuous-sheet coating designations correctly before specifying coil for exterior or formed products.
Answer first
The short answer
G60 and G90 are zinc coating designations used with ASTM A653 continuous galvanized steel sheet, not generic names for every galvanized product. The designation uses a total coating mass basis on both sides. Selection depends on substrate, thickness, formed product, cut edges, paint system, moisture, corrosivity, handling damage and service life. Do not equate G90 sheet with after-fabrication hot-dip galvanized structural steel.
Technical explanation
What controls the result
Continuous coil galvanizing and after-fabrication batch hot-dip galvanizing are different processes and coating systems.
The designation must be read with the controlling standard and its inspection language.
Roofing, ductwork, appliance and outdoor formed duty can require different coating and paint controls.
Decision table
G60 and G90 purchasing controls
| Decision factor | First option | Second option |
|---|---|---|
| Meaning | ASTM A653 continuous-sheet designation | ASTM A653 continuous-sheet designation |
| Coating basis | Read total coating mass and standard requirements | Read total coating mass and standard requirements |
| Order decision | Confirm service, paint, cuts and forming | Confirm service, paint, cuts and forming |
This table is a screening tool; order acceptance still follows the governing standard, approved sample and inspection documents.
Selection workflow
From service to an auditable specification
Define service environment, product form, fabrication and design life before comparing nominal designations.
State the governing standard, dimensions, tolerances, delivery condition and acceptance criteria in the RFQ.
Confirm finish, processing, documents, inspection and traceability before releasing the order.
Compare supplier offers to one written specification, not alloy name or price alone.
Limitations
What this guide cannot decide alone
- Typical comparisons are screening tools; the ordered standard and certified lot data control acceptance.
- Similar grades and coatings are not automatically interchangeable without reviewing environment, product form and fabrication.
- Do not infer corrosion life from a single composition, coating designation or trade name.
Procurement checklist
Make supplier offers comparable
Grade/coating system and governing product standard
Product form, dimensions, tolerances and delivery condition
Surface, metallic coating, paint system or protective film
Inspection documents, tests, marking and traceability
Quantity, packing, shipment terms and destination
Evidence
Sources and review
Project specifications and the current governing editions supersede this general guide.
ASTM International · Current ordered edition controls
American Galvanizers Association · Technical comparison
American Galvanizers Association · ASTM coating specification guide
Attributable sourcing request
Specify galvanized coil with the correct coating basis
Send standard, G designation, dimensions, end use, paint/processing, environment, quantity and destination.