What are the casing sizes
Apr 02, 2026
API 5CT casing has an outer diameter ranging from 114.3 mm to 508 mm, and a wall thickness typically between 3.18 mm and 22.2 mm. Lengths are available in three grades: R1 (4.88–7.62 m), R2 (7.62–10.36 m), and R3 (over 10.36 m).
These dimensions must conform to the latest technical specifications of API SPEC 5CT, version 11 (released December 2023), published by the American Petroleum Institute (API), to ensure safe use in deep wells, ultra-deep wells, and corrosive environments.
Complete API 5CT Casing Size Chart: Full OD 4 1/2" to 20" & All Wall Thicknesses.
API 5CT Casing Outer Diameter (OD) Specification
| Nominal Size (inch) | Outer Diameter (inch) | Outer Diameter (mm) |
| 4 1/2" | 4.500 | 114.30 |
| 5" | 5.000 | 127.00 |
| 5 1/2" | 5.500 | 139.70 |
| 6 5/8" | 6.625 | 168.28 |
| 7" | 7.000 | 177.80 |
| 7 5/8" | 7.625 | 193.68 |
| 8 5/8" | 8.625 | 219.08 |
| 9 5/8" | 9.625 | 244.48 |
| 10 3/4" | 10.750 | 273.05 |
| 11 3/4" | 11.750 | 298.45 |
| 13 3/8" | 13.375 | 339.72 |
| 16" | 16.000 | 406.40 |
| 18 5/8" | 18.625 | 473.08 |
| 20" | 20.000 | 508.00 |
API 5CT Casing Wall Thickness (WT) & Weight
| OD (inch) | Common Nominal Weight (lb/ft) | Wall Thickness (mm) |
| 4 1/2" | 9.50 / 11.60 / 13.50 | 5.21 / 6.35 / 7.37 |
| 5 1/2" | 15.50 / 17.00 / 20.00 / 23.00 | 6.71 / 7.52 / 8.94 / 10.59 |
| 7" | 23.00 / 26.00 / 29.00 / 32.00 / 35.00 | 8.05 / 9.19 / 10.36 / 11.51 / 12.65 |
| 9 5/8" | 36.00 / 40.00 / 43.50 / 47.00 / 53.50 | 8.94 / 10.03 / 11.05 / 11.99 / 13.84 |
| 13 3/8" | 48.00 / 54.50 / 61.00 / 68.00 / 72.00 | 8.38 / 9.65 / 10.92 / 12.19 / 13.06 |
| 20" | 94.00 / 106.50 / 133.00 | 11.13 / 12.70 / 16.13 |
API 5CT Casing Length Ranges
| Length Range | Range in Feet (ft) | Range in Meters (m) |
| Range 1 (R1) | 16.0 – 25.0 | 4.88 – 7.62 |
| Range 2 (R2) | 25.0 – 34.0 | 7.62 – 10.36 |
| Range 3 (R3) | 34.0 – Above | 10.36 – Above |
API Standard Casing Connections
| Abbr. | Full Name | Thread Form | Key Features | Primary Applications |
| STC | Short Round Thread | Round (V-shape), 8 TPI | Easy to stab and make up. Lower cost. Sealing relies on thread compound. | Shallow wells, low-pressure environments, low tensile load. |
| LTC | Long Round Thread | Round (V-shape), 8 TPI | Longer thread length than STC; improved tensile strength and leak resistance. | Medium-depth wells; the industry standard for conventional casing. |
| BTC | Buttress Thread | Trapezoidal, 5 TPI | Superior tensile strength and resistance to longitudinal pull. High load capacity. | Deep wells, large diameter casings, or heavy casing strings. |
Premium Connections
| Type | Key Advantages | Technical Features | Common Brands/Series |
| Gas-Tight | 100% Leak Resistance | Features a dedicated Metal-to-Metal (M-M) seal area. | VAM TOP, TenarisHydril Blue, Hunting Seal |
| Flush / Semi-Flush | Low Clearance / Smooth OD | Connection OD is equal to or slightly larger than pipe OD; reduces downhole friction. | VAM FJL, TenarisHydril CS, Wedge 513 |
| High Torque | Extreme Torsional Strength | Incorporates a Torque Shoulder to prevent over-threading. | Casing Drilling, Horizontal Wells, Extended Reach Wells. |
GNEE API 5CT Casing in stock
Real-Time Stock Update: Range 2 & Range 3 API 5CT Casings Ready for Immediate Global Shipping.
FAQ
What is the tolerance for API casing?
The 0.875 factor represents the allowable manufacturer's tolerance of minus 12.5% on wall thickness per API specifications.
What is the OD tolerance of API 5CT?
From API 5CT, OD tolerance for pipe smaller than 4.5″ is +/- 0.031″ (0.019 mm). For 4.5″ or larger, OD tolerance is +1.00%, -0.5%.
What is API 5CT?
API 5CT is a specification developed by the American Petroleum Institute (API) for casing and tubing materials used in the oil and gas industry. It includes various grades designed to meet different operational and environmental challenges.
