GFRP rebar size chart
Nominal diameters, areas and calculated weights for ASTM D7957 bar sizes and the metric diameters F1 quotes, with the steel bar of the same size beside each one.
- ASTM sizes
- No. 2–No. 10
- Metric sizes
- Ø6–Ø36 mm
- Weight vs steel
- ≈ 1/4
Last updated
How GFRP rebar sizes are named
ASTM D7957 glass fiber reinforced polymer (GFRP) bars use the inch-pound designations of steel rebar: the number is the nominal diameter in eighths of an inch, so a No. 4 bar is 1/2 in (12.7 mm). The series adds a No. 2 bar at 1/4 in. Metric suppliers name bars by nominal diameter instead, and the F1 GFRP rebar range is quoted from 6 mm to 36 mm.
A designation fixes the nominal area that strength and design values refer to. It does not make a GFRP bar interchangeable with a steel bar of the same number: the reinforcement is designed for GFRP stiffness, bond and creep rules. The GFRP rebar calculator converts certificate values into ACI CODE-440.11-22 design strengths.
ASTM D7957 GFRP bar sizes and weights 9 sizes
| Bar size | Ø in | Ø mm | Area in² | Area mm² | GFRP lb/ft | GFRP kg/m | Steel lb/ft |
|---|---|---|---|---|---|---|---|
| No. 2 | 0.250 | 6.4 | 0.05 | 32 | 0.041 | 0.061 | 0.169 |
| No. 3 | 0.375 | 9.5 | 0.11 | 71 | 0.091 | 0.135 | 0.375 |
| No. 4 | 0.500 | 12.7 | 0.20 | 129 | 0.165 | 0.245 | 0.681 |
| No. 5 | 0.625 | 15.9 | 0.31 | 199 | 0.254 | 0.378 | 1.050 |
| No. 6 | 0.750 | 19.1 | 0.44 | 284 | 0.363 | 0.540 | 1.498 |
| No. 7 | 0.875 | 22.2 | 0.60 | 387 | 0.494 | 0.735 | 2.042 |
| No. 8 | 1.000 | 25.4 | 0.79 | 510 | 0.651 | 0.969 | 2.690 |
| No. 9 | 1.128 | 28.7 | 1.00 | 645 | 0.824 | 1.226 | 3.403 |
| No. 10 | 1.270 | 32.3 | 1.27 | 819 | 1.046 | 1.556 | 4.320 |
Calculated weights, not declared values. The density basis follows the specific gravity of 1.92 measured on GFRP bars in a University of Kentucky study for FHWA; resin, glass content and surface treatment change the actual mass, so use the supplier's declared mass per foot for freight and handling.
Metric GFRP rebar diameters on the F1 inquiry list 15 diameters
| Diameter | Area mm² | GFRP kg/m | GFRP lb/ft | Steel kg/m | Closest ASTM |
|---|---|---|---|---|---|
| Ø6 mm | 28 | 0.053 | 0.036 | 0.220 | No. 2 |
| Ø8 mm | 50 | 0.095 | 0.064 | 0.393 | No. 3 |
| Ø10 mm | 79 | 0.150 | 0.101 | 0.620 | No. 3 |
| Ø12 mm | 113 | 0.215 | 0.144 | 0.887 | No. 4 |
| Ø14 mm | 154 | 0.293 | 0.197 | 1.209 | No. 4 |
| Ø16 mm | 201 | 0.382 | 0.257 | 1.578 | No. 5 |
| Ø18 mm | 254 | 0.483 | 0.324 | 1.994 | No. 6 |
| Ø20 mm | 314 | 0.597 | 0.401 | 2.465 | No. 6 |
| Ø22 mm | 380 | 0.722 | 0.485 | 2.983 | No. 7 |
| Ø25 mm | 491 | 0.933 | 0.627 | 3.854 | No. 8 |
| Ø28 mm | 616 | 1.170 | 0.787 | 4.836 | No. 9 |
| Ø30 mm | 707 | 1.343 | 0.903 | 5.550 | No. 9 |
| Ø32 mm | 804 | 1.528 | 1.027 | 6.311 | No. 10 |
| Ø34 mm | 908 | 1.725 | 1.159 | 7.128 | No. 10 |
| Ø36 mm | 1018 | 1.934 | 1.300 | 7.991 | No. 10 |
Using the chart for an inquiry or a shipment
Reading a drawing. Take the bar size and spacing from the GFRP design, not from a steel drawing. If a drawing gives metric diameters and the supplier quotes ASTM sizes, or the reverse, ask for the certified area of the offered bar and have the designer confirm the substitution.
Comparing offers. Two bars sold as the same size can differ in core diameter, surface and guaranteed tensile load. Compare the certified area, guaranteed tensile force, modulus and the edition of ASTM D7957 the reports were run against. The GFRP rebar specification guide lists the submittal documents, and the fiberglass rebar cost guide shows how to compare price per foot on the same basis.
Planning freight and handling. Multiply the declared mass per foot by the scheduled lengths and add bent shapes separately. GFRP bundles are light but flexible, so lifting still needs a spreader bar and several pick-up points, as the installation guide explains.
GFRP rebar size questions
What sizes does GFRP rebar come in?
In the United States, ASTM D7957 GFRP bars use the same number designations as steel rebar, from No. 2 (1/4 in) to No. 10 (1.27 in), with No. 2 as an extra small size. Metric suppliers list nominal diameters; the F1 inquiry list runs from 6 mm to 36 mm. Larger and intermediate sizes depend on the supplier and the grade offered.
How much does GFRP rebar weigh compared with steel?
About a quarter of the weight of a steel bar of the same nominal size. At a density of 1.9 g/cm³ a No. 4 GFRP bar is calculated at about 0.16 lb/ft (0.25 kg/m), against about 0.68 lb/ft for steel at 7.85 g/cm³. Use the supplier's declared mass for shipping and handling plans.
Is a No. 4 GFRP bar a direct replacement for a No. 4 steel bar?
No. The designation only describes the nominal size. GFRP has roughly a quarter of the stiffness of steel and no yield plateau, so the engineer of record sizes and spaces the bars to ACI CODE-440.11-22, CSA S806 or the code adopted for the project. The chart helps read drawings and prepare an inquiry.
Why is the measured diameter of a GFRP bar larger than its nominal size?
Ribs, a helical wrap or a sand coating sit outside the load-bearing core, so a caliper across the surface reads more than the nominal diameter. Strength and design values are tied to the nominal area for the designation. When two offers name the same size, compare the certified area and guaranteed tensile load rather than the outside diameter.
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