A 1 1/4 inch steel tubing label is a size class, not one fixed measurement — that pipe size is 1.660 in OD, while a tube is often 1.250 in.
Two steel products stamped 1 1/4 inch can land almost half an inch apart: 1.660 in OD for pipe, 1.250 in for tube. Ordering the right length comes down to three numbers — outside diameter (OD), wall thickness, and inside diameter (ID). A tape measure and a caliper settle what the label cannot. Here are the dimensions behind the 1 1/4 in size class, the wall-thickness ranges, and a measuring routine that repeats.
1 1/4 Inch Steel Tubing: What The Label Leaves Out
Pipe sizes are nominal — the number sits close to neither the outside nor the inside diameter — while tubing is normally specified by actual outside diameter and wall thickness.
Alro’s steel tube and pipe guide lists 1-1/4 in standard wall pipe at 1.660 in OD, 0.140 in wall, 1.380 in ID, and 2.27 lb per foot. The same guide’s tube table shows a 1-1/4 in entry at 1.250 in OD. Identical wording on an invoice, parts that will not swap.
| Dimension Or Detail | 1-1/4 In Pipe | 1-1/4 In Tubing |
|---|---|---|
| Outside diameter | 1.660 in (42.16 mm) | 1.250 in |
| What the label describes | Nominal pipe size | Actual outside diameter |
| Inside diameter | 1.380 in at standard wall | OD minus twice the wall |
| Common wall thickness | 0.140 in | 0.028 in to 0.095 in |
| Weight per foot | 2.27 lb | Varies with wall thickness |
| How it is ordered | By nominal size and schedule | By outside diameter and wall |
Our tested picks for 1 1/4 inch steel tubing list the outside diameters and wall thicknesses each option ships in, so a quick comparison against your own readings narrows the field.
Wall Thickness Decides What Fits
Wall thickness quietly breaks replacement jobs. It sets the inside diameter, flow area, and weight per foot, so two tubes with the same 1.250 in OD can have different inside diameters the moment the wall changes.
Common imperial walls include 0.028, 0.035, 0.049, 0.065, 0.083, and 0.095 in; the full span runs from 0.020 in to 0.375 in. ASTM A269 covers seamless and welded austenitic stainless steel tubing for general service, furnishing sizes from 1/4 in ID and larger with a nominal wall of 0.020 in and heavier. For heat exchangers, ASTM A179 covers seamless cold-drawn low-carbon steel tubes from 1/8 to 3 in OD.
Weight per foot follows the wall — extra metal adds pounds without changing the outside diameter, which matters in a frame with a weight limit. Stainless, welded, and seamless tubing each carry their own wall options, so a listing naming only an outside diameter leaves the fit undecided. If the wall is missing, ask for it, or for the inside diameter your fitting needs, before you pay.
How Do You Measure Steel Tubing Correctly?
Measure at least 2 in from either end and keep the caliper off the weld line. PA Steel’s steel tubing handbook calls for outside-diameter readings 90 degrees to the weld line and on either side of it, skipping the weld itself unless the customer asks otherwise.
The 2 in setback exists because saw-cut ends distort slightly, and a reading at the edge can run small. Without a caliper, wrap a tape around the tube, divide the circumference by pi, and compare to the expected OD. With calipers, measure at a square, undamaged end first, then repeat two or three times along the length.
Three readings within a few thousandths of an inch of each other tell you the number is trustworthy. A sudden jump usually means an out-of-round spot, a burr, or a weld seam caught under the jaws.
Before ordering, collect four items: outside diameter, wall thickness, inside diameter, and the grade or standard the job calls for. Mixing nominal pipe size with tube OD is the mistake that sends material back — 1-1/4 in pipe is 1.660 in OD, not 1.25 in, and a 1-1/4 in tube is usually 1.250 in OD. Hand those four numbers to the supplier and the paperwork matches on the first try.
FAQs
Is 1-1/4 in pipe the same as 1.250 in tube?
No. Pipe at the 1-1/4 in callout measures 1.660 in across the outside with a 0.140 in wall in standard weight, putting the inside diameter at 1.380 in. A tube listed at 1-1/4 in usually measures 1.250 in OD. The two will not interchange inside a fitting, coupling, or bushing.
How do I choose a wall thickness?
Work backward from the inside diameter your fitting, bushing, or flow path needs, then pick the wall that produces it. Common tubing walls run 0.028 in to 0.095 in, with heavier options reaching 0.375 in. When a listing shows only the outside diameter, request the wall thickness before you buy.
Can I measure a tube with a tape measure instead of calipers?
Yes, as a cross-check. Wrap the tape snugly around the tube, divide the circumference by 3.1416, and compare the result to the outside diameter you expected. That method is accurate enough to sort 1.250 in tube from 1.660 in pipe, but for fabrication work use calipers and take readings at least 2 in from the ends.
References & Sources
- ASTM International. “ASTM A269/A269M-15a: Seamless and Welded Austenitic Stainless Steel Tubing.” Defines the standard’s scope and its nominal wall and size floors.
- Alro Steel. “Steel Tube & Pipe Reference Guide.” Source of the 1-1/4 in pipe OD, wall, ID, and weight-per-foot figures and the 1.250 in tube entry.
- PA Steel. “Steel Tubing Handbook.” Source of the tolerance and outside-diameter measuring guidance.
