Steam hose pipe sizes from 1/2 inch to 2 inch, with bore, OD and pressure
Six bores, two grades, and a different outside diameter for each combination. Here is the full size chart, why the coupling follows the outside of the hose, and how to measure an old length before you reorder.
Flexihose rubber steam hose: one wire braid 1/2" to 2" (12.50 to 50.00 mm), mean OD 21.50 to 64.50 mm, 145 PSI / 10 BAR · two wire braid 1/2" to 1-1/4" (12.50 to 31.00 mm), mean OD 24.00 to 45.00 mm, 250 PSI / 17 BAR · same pressure at every bore within a grade
Quick answer
Flexihose catalogues rubber steam hose by bore, from 1/2 inch (12.50 mm) to 2 inch (50.00 mm). The one wire braid grade covers all six sizes at 10 BAR, and the two wire braid grade covers 1/2 inch to 1-1/4 inch at 17 BAR. Every size has its own mean outside diameter in each grade, and that outside figure, not the bore, is what a steam coupling has to fit.
A steam hose is ordered by its bore, but it is fitted by its outside diameter, and the two do not move together. A 1" hose with one wire braid and a 1" hose with two braids share a bore and differ by 2.5 mm on the outside, which is enough to make a coupling sized for one leak on the other. We make both grades at our works in Bhiwadi, and we publish the mean OD for every size for exactly this reason. This guide covers the full size chart for both grades, why couplings follow the mean OD, how to measure an old hose when you replace it, and which sizes are not made at 17 BAR.
Steam hose size chart for the one braid and two braid grades
Every figure in the chart is transcribed from our 2026-2027 catalogue. Pressure does not change with size inside a grade: the one wire braid grade is 145 PSI / 10 BAR working and 1450 PSI / 100 BAR minimum burst at every bore, and the two wire braid grade is 250 PSI / 17 BAR working and 2500 PSI / 170 BAR minimum burst at every bore. What changes with size is the outside diameter.
Steam hose sizes, 1/2" to 2", both grades. Mean OD is the figure to give your coupling supplier.
| Size | Bore | One braid mean OD | Two braid mean OD | One braid WP / burst | Two braid WP / burst |
|---|---|---|---|---|---|
| 1/2" | 12.50 mm | 21.50 mm | 24.00 mm | 10 / 100 BAR | 17 / 170 BAR |
| 3/4" | 20.00 mm | 29.00 mm | 31.00 mm | 10 / 100 BAR | 17 / 170 BAR |
| 1" | 25.00 mm | 35.50 mm | 38.00 mm | 10 / 100 BAR | 17 / 170 BAR |
| 1-1/4" | 31.00 mm | 42.50 mm | 45.00 mm | 10 / 100 BAR | 17 / 170 BAR |
| 1-1/2" | 38.00 mm | 50.50 mm | Not catalogued | 10 / 100 BAR | Ask |
| 2" | 50.00 mm | 64.50 mm | Not catalogued | 10 / 100 BAR | Ask |
Source: FLEXI HOSE Product Catalogue 2026-2027. In PSI, 10 / 100 BAR is printed as 145 / 1450 PSI and 17 / 170 BAR as 250 / 2500 PSI. Service temperature: −40 °C to +195 °C one braid, −40 °C to +232 °C two braid. Coil and cut lengths are not printed in the catalogue and are confirmed with each quote.
Drawn to one scale, the chart becomes easier to read. In the figure below, each ring is a cross-section of the hose: the pale centre is the bore, the dark ring is the one braid wall, and the dashed outline shows where the two braid wall finishes for the four sizes made in that grade.
The six catalogued bores in section, drawn to relative scale. The dashed outline is the two wire braid mean OD.
Dimensions from the FLEXI HOSE Product Catalogue 2026-2027, drawn at one scale. Braid layers are not drawn individually.
1. 1/2 inch and 3/4 inch steam hose
The two smallest bores are made in both grades. A 1/2" hose has a 12.50 mm bore and a mean OD of 21.50 mm with one braid or 24.00 mm with two. A 3/4" hose has a 20.00 mm bore and a mean OD of 29.00 mm or 31.00 mm. Because the pressure rating is the same at every bore in a grade, choosing between 1/2" and 3/4" is a question of the connection and the flow you need, not of pressure.
2. 1 inch steam hose
A 1" steam hose has a 25.00 mm bore. With one wire braid its mean OD is 35.50 mm, rated 145 PSI / 10 BAR working and 1450 PSI / 100 BAR minimum burst. With two braids it is 38.00 mm, rated 250 PSI / 17 BAR working and 2500 PSI / 170 BAR minimum burst. Both are on our steam hose page with their full specification.
3. 1-1/4 inch steam hose
The largest size made in both grades: 31.00 mm bore, 42.50 mm mean OD with one braid and 45.00 mm with two. If your duty needs the two braid grade, 1-1/4" is the top of the catalogued range, and anything larger at 17 BAR is a question for the works.
4. 1-1/2 inch and 2 inch steam hose
These two are catalogued in the one wire braid grade only. A 1-1/2" hose has a 38.00 mm bore and a 50.50 mm mean OD; a 2" hose has a 50.00 mm bore and a 64.50 mm mean OD. Both carry the same 10 BAR working and 100 BAR minimum burst as the 1/2". The last section explains what to do if you need either size at 17 BAR.
Why steam hose couplings are matched to mean OD, not bore
A steam coupling has two jobs. Its tail sits inside the bore, and its ferrule or shell grips the outside of the hose, pressing the wall onto the tail. The grip is what holds the joint against pressure, and the grip is set by the outside diameter. Two hoses with the same bore but different walls need different ferrules.
That is exactly the case between our two grades. The second braid adds wall, so at every shared size the two braid hose is larger on the outside. The bore is identical; the fit is not.
Two 1" steam hoses in section at the same scale. Same bore, different outside diameter.
Bore and mean OD from the FLEXI HOSE Product Catalogue 2026-2027. Wall thickness is calculated as (mean OD − bore) ÷ 2. Dashed rings mark the number of braids, not their exact position in the wall.
The same arithmetic across the whole range gives the wall thickness for each size. It is a calculated figure, half the difference between mean OD and bore, and it shows why a ferrule sized for one grade does not suit the other.
| Size | One braid wall | Two braid wall | OD difference between grades |
|---|---|---|---|
| 1/2" | 4.50 mm | 5.75 mm | 2.50 mm |
| 3/4" | 4.50 mm | 5.50 mm | 2.00 mm |
| 1" | 5.25 mm | 6.50 mm | 2.50 mm |
| 1-1/4" | 5.75 mm | 7.00 mm | 2.50 mm |
| 1-1/2" | 6.25 mm | Not catalogued | Not applicable |
| 2" | 7.25 mm | Not catalogued | Not applicable |
Two practical rules follow. When you order couplings separately, give the supplier the grade as well as the size, or better, the mean OD itself. And use couplings that grip the wire: interlocking or crimped steam couplings. A worm-drive clamp on a barbed tail is not a steam fitting, because the wall expands as the line heats and contracts as it cools, and a screw clamp does not follow it. If you would rather not match parts yourself, we supply the made-up assembly with ends fitted at our works. Our guide to reading steam hose specifications covers the other lines a coupling order depends on.
How to measure an old steam hose when you replace it
Replacement orders go wrong when the size is guessed from the outside of a worn hose. The bore tells you the size; the outside diameter tells you the grade. Measure both, in this order, on a hose that is isolated and cold.
- Step 1Isolate and coolShut off, vent and let the hose cool fully.
- Step 2Read the markingSize and grade printed on the cover, if legible.
- Step 3Measure the boreAt a clean cut end, not through a fitting.
- Step 4Measure the ODTape round the cover, divide by 3.1416.
- ResultSize and gradeMatch both figures to the chart.
Procedure based on the published Flexihose guidance to measure the inside diameter of a hose being replaced, and on the mean OD figures in the size chart.
1. Isolate the line, vent it and let the hose cool
Close the supply valve, release the pressure trapped in the hose and leave it until it is cold to the touch. Never uncouple a steam hose that is still under pressure or still hot; residual steam and condensate are enough to scald.
2. Read whatever the cover still says
If the printed marking along the cover is legible, note the size, the grade and any standard it names. ISO 6134, the international specification for rubber steam hose, includes a marking clause for hoses and couplings (ISO 6134:2024 contents). On an old hose the print has often worn away, which is why the next two measurements matter.
3. Measure the bore at a clean cut end
Measure the inside diameter, not the outside. Use inside callipers or a bore gauge on a square cut through undamaged hose. Do not measure through a coupling: the coupling tail sits inside the bore and reads smaller than the hose. Round to the nearest catalogued bore: 12.50, 20.00, 25.00, 31.00, 38.00 or 50.00 mm.
4. Measure the outside diameter with a tape
Wrap a flexible tape around an undamaged section of cover, read the circumference, and divide by 3.1416. A vernier across the hose works too, but take two readings at right angles and average them, because a hose that has been clamped or stored flat is rarely perfectly round. The formal methods are written down in IS 15913:2011, the Indian standard on measuring the dimensions of rubber and plastics hoses, and in ISO 4671, which carries the same title (BIS cross-reference list).
5. Match both figures to the chart, then measure the length
The bore gives you the size. The OD tells you whether it is one braid or two. For example, a tape reading of 119 mm divides to 37.9 mm, which matches the 38.00 mm mean OD of our 1" two wire braid grade. If your reading falls between two catalogued figures, trust the bore for the size and send us both numbers. Finish by measuring the overall length, including couplings if you want a made-up assembly, and note the coupling type at each end.
Expected tape readings around the cover for each size and grade, calculated from the mean OD.
| Size | One braid: mean OD | One braid: circumference | Two braid: mean OD | Two braid: circumference |
|---|---|---|---|---|
| 1/2" | 21.50 mm | 67.5 mm | 24.00 mm | 75.4 mm |
| 3/4" | 29.00 mm | 91.1 mm | 31.00 mm | 97.4 mm |
| 1" | 35.50 mm | 111.5 mm | 38.00 mm | 119.4 mm |
| 1-1/4" | 42.50 mm | 133.5 mm | 45.00 mm | 141.4 mm |
| 1-1/2" | 50.50 mm | 158.7 mm | Not catalogued | |
| 2" | 64.50 mm | 202.6 mm | Not catalogued | |
Mean OD from the FLEXI HOSE Product Catalogue 2026-2027. Circumference calculated as mean OD × 3.1416 and rounded to 0.1 mm. The catalogue does not print an OD tolerance, so treat these as targets, not limits.
Which steam hose sizes are not made at 17 BAR, and what to do instead
Our two wire braid grade is catalogued from 1/2" to 1-1/4". We do not quote a pressure for 1-1/2" or 2" at 17 BAR, because the catalogue does not print one, and we will not tell you those sizes cannot be made either. If your line needs a large bore at a pressure or temperature above the one braid grade’s limits, these are the routes to discuss.
Options when you need 1-1/2" or 2" above 10 BAR or +195 °C.
| Option | When it fits | What we can confirm | Status |
|---|---|---|---|
| Recheck the duty at the hose | The 17 BAR figure came from the boiler, not the hose point | If the hose sees 10 BAR or less and +195 °C or less, the one braid grade is catalogued at 1-1/2" and 2" | Start here |
| Ask the works | The duty genuinely needs the two braid grade in a larger bore | We answer from the works rather than quote an unprinted rating | Enquire |
| PTFE hose | Temperature above +232 °C, or steam with aggressive chemicals | Catalogued −65 °C to +260 °C, 1/8" to 2"; 30 BAR at 2", with pressure read at your bore | Check bore |
| Stainless steel corrugated hose | Metal connections, or bores above 2" | EN ISO 10380, 6 to 150 mm; pressure falls with bore; service temperature confirmed against your duty | Check duty |
Source: FLEXI HOSE Product Catalogue 2026-2027. The catalogue prints PTFE and stainless steel pressures only at the ends of each range, so ask for the rating at your exact bore.
The first row matters more than it looks. A line described as 17 BAR may be 17 BAR at the boiler and lower at the hose point, after a reducing station. If the pressure at the hose is 10 BAR or less and the temperature at the hose is +195 °C or less, the one wire braid grade covers 1-1/2" and 2" on its published rating. Superheated steam changes this: it can run above +195 °C at moderate pressure, and then temperature, not pressure, decides the grade.
Whatever route you take, the rubber grades are for steam and condensate only. They are not for hot oil or thermal fluid, which attack EPDM, they carry no food or pharmaceutical grade, and they do not replace fixed steam piping. If your tender names a standard for the larger bore, our guide to IS 10655 and steam hose claims explains what our grades do and do not claim.
Measure the bore, check the OD, then ask for your size
Order a steam hose by its bore, fit it by its mean OD, and choose the grade on the pressure and temperature at the hose. Our one wire braid grade covers every size from 1/2" to 2" at 10 BAR; the two wire braid grade covers 1/2" to 1-1/4" at 17 BAR, and larger sizes at that rating are a question for the works. Send the bore, the OD you measured and the duty, and we will confirm the size and grade at Flexihose.
FAQ
What are the standard steam pipe sizes?
Rigid steam pipe is sized by nominal bore and wall schedule, not by outside diameter alone. Spirax Sarco notes that Schedules 40 and 80 are the only ones covering the full range from 15 mm to 600 mm nominal size, and that they are the most commonly used for steam pipe installations.
What are the different types of steam pipes?
Steam pipe is usually grouped by material and joint. Spirax Sarco describes carbon steel to ASTM A106 for welded mains, red band screwed pipe to EN 10255 for smaller threaded work, chromium-molybdenum steel for superheated service and copper for condensate. Mains, branch lines and condensate returns each follow the plant code.
What are the technical specifications for hose pipes?
A hose specification lists bore, outside diameter, working pressure, minimum burst pressure, temperature range, reinforcement, tube and cover materials, and the standard it is built to. Record the grade as well as the bore, because two steam hoses of the same bore can carry different ratings and outside diameters.
What pipe is used for steam?
Fixed runs use rigid pipe, normally carbon steel, and Spirax Sarco notes that Schedules 40 and 80 cover 15 mm to 600 mm nominal. The last flexible connection is hose: rubber steam hose from 1/2 to 2 inch bore, or corrugated stainless steel hose where bores reach 150 mm.
What are steam lines?
They are the network of pipes that carry steam from the boiler to the equipment that uses it. Spirax Sarco notes that steam is usually generated at a pressure of at least 7 bar g, because higher pressure lets the distribution pipes be kept to a reasonable size for the heat they carry.
Have a question this guide didn't answer?
Send us your bore size, pressure and application and we'll recommend the right hose.