Tube and Pipe Sizes
Round mechanical tube (DOM and ERW) by outside diameter and wall gauge, common square and rectangular tube and HSS, and the difference that trips up most first orders: tube is named by its real OD, pipe by a nominal size.
Tube vs pipe
| Tube | Pipe | |
|---|---|---|
| Sized by | Actual outside diameter and wall (decimal or gauge) | Nominal pipe size (NPS) and schedule |
| Does the name equal the OD? | Yes: 1 in tube is 1.000 in OD | Only from NPS 14 up; NPS 1 is 1.315 in OD |
| Wall | Chosen freely from the gauge or decimal walls | Set by schedule, and the same schedule is a different wall at each NPS |
| Tolerance focus | OD, wall and straightness for machining and fit-up | Pressure rating, weldability and threading |
| Typical specs | ASTM A513 (ERW and DOM), A519 (seamless), A500 / A1085 (HSS), A269 (stainless) | ASTM A53, A106 (carbon), A312 (stainless); dimensions per ASME B36.10M / B36.19M |
| Typical uses | Frames, structures, bushings, cylinders, machined sleeves | Fluid and gas piping, pressure systems, posts and bollards |
Nominal pipe size vs actual OD
Up to NPS 12 a pipe is always bigger than its name. From NPS 14 the OD equals the NPS. Walls by schedule are in the pipe schedule chart.
| NPS | DN | Pipe OD (in) | Pipe OD (mm) | Larger than a same-name tube by (in) |
|---|---|---|---|---|
| 1/8 | 6 | 0.405 | 10.3 | 0.280 |
| 1/4 | 8 | 0.540 | 13.7 | 0.290 |
| 3/8 | 10 | 0.675 | 17.1 | 0.300 |
| 1/2 | 15 | 0.840 | 21.3 | 0.340 |
| 3/4 | 20 | 1.050 | 26.7 | 0.300 |
| 1 | 25 | 1.315 | 33.4 | 0.315 |
| 1-1/4 | 32 | 1.660 | 42.2 | 0.410 |
| 1-1/2 | 40 | 1.900 | 48.3 | 0.400 |
| 2 | 50 | 2.375 | 60.3 | 0.375 |
| 2-1/2 | 65 | 2.875 | 73.0 | 0.375 |
| 3 | 80 | 3.500 | 88.9 | 0.500 |
| 3-1/2 | 90 | 4.000 | 101.6 | 0.500 |
| 4 | 100 | 4.500 | 114.3 | 0.500 |
| 5 | 125 | 5.563 | 141.3 | 0.563 |
| 6 | 150 | 6.625 | 168.3 | 0.625 |
| 8 | 200 | 8.625 | 219.1 | 0.625 |
| 10 | 250 | 10.750 | 273.1 | 0.750 |
| 12 | 300 | 12.750 | 323.8 | 0.750 |
Tube wall gauges (BWG)
| Gauge | Wall (in) | mm |
|---|---|---|
| 22 | 0.028 | 0.71 |
| 20 | 0.035 | 0.89 |
| 18 | 0.049 | 1.24 |
| 16 | 0.065 | 1.65 |
| 14 | 0.083 | 2.11 |
| 13 | 0.095 | 2.41 |
| 12 | 0.109 | 2.77 |
| 11 | 0.120 | 3.05 |
| 10 | 0.134 | 3.40 |
| 8 | 0.165 | 4.19 |
| 7 | 0.180 | 4.57 |
Round tube ODs commonly stocked
DOM and ERW mechanical tube, OD in inches with the mm equivalent.
- 1/46.35 mm
- 5/167.94 mm
- 3/89.52 mm
- 1/212.70 mm
- 5/815.88 mm
- 3/419.05 mm
- 7/822.22 mm
- 125.40 mm
- 1-1/828.58 mm
- 1-1/431.75 mm
- 1-3/834.93 mm
- 1-1/238.10 mm
- 1-5/841.28 mm
- 1-3/444.45 mm
- 250.80 mm
- 2-1/457.15 mm
- 2-1/263.50 mm
- 376.20 mm
- 3-1/288.90 mm
- 4101.60 mm
- 5127.00 mm
- 6152.40 mm
Not every OD comes in every wall: thin walls are mostly on the small ODs, heavy walls on the large ones.
Common round tube sizes
| OD x wall (in) | Gauge | ID (in) | OD x wall (mm) | Steel lb/ft | Typical use |
|---|---|---|---|---|---|
| 1/2 x 0.049 | 18 ga | 0.402 | 12.70 x 1.24 | 0.24 | Light frames, handles, spacers |
| 1/2 x 0.065 | 16 ga | 0.370 | 12.70 x 1.65 | 0.30 | Bushings, light brackets |
| 3/4 x 0.065 | 16 ga | 0.620 | 19.05 x 1.65 | 0.48 | Railings, light frames |
| 3/4 x 0.120 | 11 ga | 0.510 | 19.05 x 3.05 | 0.81 | Bushings and sleeves |
| 1 x 0.065 | 16 ga | 0.870 | 25.40 x 1.65 | 0.65 | Frames, guards, carts |
| 1 x 0.095 | 13 ga | 0.810 | 25.40 x 2.41 | 0.92 | Frames, linkages |
| 1 x 0.120 | 11 ga | 0.760 | 25.40 x 3.05 | 1.13 | Structural frames, bushings |
| 1-1/4 x 0.083 | 14 ga | 1.084 | 31.75 x 2.11 | 1.04 | Frames, tube bending |
| 1-1/4 x 0.120 | 11 ga | 1.010 | 31.75 x 3.05 | 1.45 | Heavier frames |
| 1-1/2 x 0.065 | 16 ga | 1.370 | 38.10 x 1.65 | 1.00 | Light frames, handrail |
| 1-1/2 x 0.120 | 11 ga | 1.260 | 38.10 x 3.05 | 1.77 | Chassis and machine frames |
| 1-1/2 x 0.188 | 1.124 | 38.10 x 4.78 | 2.64 | Cylinder bodies, sleeves | |
| 1-3/4 x 0.120 | 11 ga | 1.510 | 44.45 x 3.05 | 2.09 | Roll cages, chassis |
| 2 x 0.083 | 14 ga | 1.834 | 50.80 x 2.11 | 1.70 | Frames, guards |
| 2 x 0.120 | 11 ga | 1.760 | 50.80 x 3.05 | 2.41 | Frames, posts |
| 2 x 0.250 | 1.500 | 50.80 x 6.35 | 4.68 | Machined sleeves, hydraulic parts | |
| 2-1/2 x 0.120 | 11 ga | 2.260 | 63.50 x 3.05 | 3.05 | Posts, frames |
| 3 x 0.120 | 11 ga | 2.760 | 76.20 x 3.05 | 3.69 | Posts, housings |
| 3 x 0.250 | 2.500 | 76.20 x 6.35 | 7.35 | Machined housings and sleeves | |
| 4 x 0.250 | 3.500 | 101.60 x 6.35 | 10.02 | Machined housings, cylinder barrels |
ID = OD - 2 x wall. Weight is plain carbon steel, 10.69 x (OD - wall) x wall lb/ft; aluminum is about one third of that.
Square and rectangular tube
| Size (in) | Size (mm) | Spec | Walls commonly stocked (in) | Walls (mm) |
|---|---|---|---|---|
| 1 x 1 | 25.4 x 25.4 | A513 | 0.065, 0.083, 0.120 | 1.65, 2.11, 3.05 |
| 1-1/2 x 1-1/2 | 38.1 x 38.1 | A513 / A500 | 0.065, 0.083, 0.120, 3/16 | 1.65, 2.11, 3.05, 4.76 |
| 2 x 2 | 50.8 x 50.8 | A513 / A500 | 0.083, 0.120, 3/16, 1/4 | 2.11, 3.05, 4.76, 6.35 |
| 3 x 3 | 76.2 x 76.2 | A500 | 1/8, 3/16, 1/4 | 3.18, 4.76, 6.35 |
| 4 x 4 | 101.6 x 101.6 | A500 | 1/8, 3/16, 1/4, 3/8, 1/2 | 3.18, 4.76, 6.35, 9.52, 12.70 |
| 6 x 6 | 152.4 x 152.4 | A500 | 3/16, 1/4, 3/8, 1/2 | 4.76, 6.35, 9.52, 12.70 |
| 8 x 8 | 203.2 x 203.2 | A500 | 1/4, 3/8, 1/2 | 6.35, 9.52, 12.70 |
| 2 x 1 | 50.8 x 25.4 | A513 | 0.065, 0.083, 0.120 | 1.65, 2.11, 3.05 |
| 3 x 2 | 76.2 x 50.8 | A500 | 1/8, 3/16, 1/4 | 3.18, 4.76, 6.35 |
| 4 x 2 | 101.6 x 50.8 | A500 | 1/8, 3/16, 1/4 | 3.18, 4.76, 6.35 |
| 6 x 2 | 152.4 x 50.8 | A500 | 3/16, 1/4 | 4.76, 6.35 |
| 6 x 4 | 152.4 x 101.6 | A500 | 3/16, 1/4, 3/8 | 4.76, 6.35, 9.52 |
| 8 x 4 | 203.2 x 101.6 | A500 | 1/4, 3/8, 1/2 | 6.35, 9.52, 12.70 |
Decimal walls (0.065, 0.083, 0.120 in) are gauge mechanical tube; fractional walls are structural HSS. For A500 HSS, AISC design uses 0.93 x the nominal wall. Outside corners have a radius of roughly two wall thicknesses, which matters for fit-up and for flat widths.
Need tube cut, bent, welded or machined? , or read about tube bending.
Ordering tube
- Give OD, wall and type. "1.500 x 0.120 DOM, A513 Type 5" is a complete callout. "1-1/2 in tube" is not: it could be read as tube of that OD or as NPS 1-1/2 pipe, which is 1.900 in OD.
- Seamless is its own product. Cold-drawn seamless mechanical tube (ASTM A519) has no seam at all and comes in heavier walls, at a price. Most frame and machined-sleeve work is fine in DOM.
- Heavy walls are for machining. A thick-wall DOM tube is often cheaper than boring a sleeve out of solid bar stock; pick an OD and ID that leave cleanup on both.
- Stainless and aluminum tube. Stainless ornamental and sanitary tube is sold by OD and wall too (ASTM A554, A269, A270); aluminum round tube (6061-T6, 6063-T52) follows the same OD and wall convention.
Related charts, tools and guides
Frequently asked questions
- What is DOM tubing?
- Drawn over mandrel. Electric-resistance-welded tube is cold drawn through a die over a mandrel, which sizes the OD and ID together, evens out the wall and works the weld seam until it is hard to find. It costs more than as-welded tube and is the usual choice for machined sleeves, cylinder bodies, bushings and roll cages.
- ERW or DOM?
- As-welded ERW tube (ASTM A513 Type 1 hot rolled or Type 2 cold rolled) is cheaper and fine for frames, guards and furniture. It has a weld seam and, unless it is flash controlled, a small bead inside. Pick DOM when the ID is a working surface, when something slides inside it, or when the wall has to be uniform for machining.
- What does 11 gauge tube mean?
- A 0.120 in wall. Tube walls follow the Birmingham wire gauge decimals: 16 ga is 0.065 in, 14 ga is 0.083 in, 11 ga is 0.120 in. They are close to, but not the same as, sheet steel gauges.
- Why is HSS thinner than its nominal wall?
- ASTM A500 lets structural tube run under its nominal wall, so AISC has designers use 0.93 times the nominal thickness for section properties. HSS made to ASTM A1085 has a tighter wall tolerance and is designed with the full nominal wall.
