Pipe Overview

“Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. “Nominal” refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for example – 2-inch nominal steel pipe” consists of many varieties of steel pipe with the only criterion being a 2.375-inch (60.3 mm) outside diameter). Specific pipe is identified by pipe diameter and another non-dimensional number for wall thickness referred to as the Schedule (Sched. or Sch., for example – “2-inch diameter pipe, Schedule 40″). The European and international designation equivalent to NPS is DN (diamètre nominal/nominal diameter/Durchmesser nach Norm), in which sizes are measured in millimetres.”

Based on the NPS and schedule of a pipe, the pipe outside diameter (OD) and wall thickness can be obtained from reference tables such as those below, which are based on ASME standards B36.10M and B36.19M. For example, NPS 14 Sch 40 has an OD of 14 inches (360 mm) and a wall thickness of 0.437 inches (11.1 mm). However the NPS and OD values are not always equal, which can create confusion.

  • For NPS ⅛ to 12, the NPS and OD values are different. For example, the OD of an NPS 12 pipe is actually 12.75 inches (324 mm). To find the actual OD for each NPS value, refer to the tables below. (Note that for tubing, the size indicates actual dimensions, not nominal.)
  • For NPS 14 and up, the NPS and OD values are equal. In other words, an NPS 14 pipe is actually 14 inches (360 mm) OD.

The reason for the discrepancy for NPS ⅛ to 12 inches is that these NPS values were originally set to give the same inside diameter (ID) based on wall thicknesses standard at the time. However, as the set of available wall thicknesses evolved, the ID changed and NPS became only indirectly related to ID and OD.

Pipe by Scale

Here we have pipe dimensions in a few of the more common scales – N (1:160), HO (1:87.1), S (1:64), US O scale (1:48), British O scale (1:43.5) and 1:24

Click the photo to open up a PDF

If there are any errors they will be in columns 3 and 4 since I manually put those numbers in. Everything else was generated through Excel formulas. If I DID fat finger anything (I .. don’t *think* I did) let me know in the comments at the bottom of the page so I can fix it.

Matching Tubing to Pipe

In the table below we are matching Evergreen tubing in the left column with the closest sized for pipe in British O scale – 1:43.5 or 7mm to the foot and US O scale of 1:48 or 1/4″ to the foot.

  • We have two main columns labeled 1:43.5 and 1:48
  • Each of the main columns have sub-columns labeled FS OD [in] (mm) which simply mean Full Scale OD in Inches and mm.
  • Sub-Column 1 – Labeled Evergreen is simply all of the Evergreen tubing sizes
  • Sub-Column 2 – Labeled FS OD [in] (mm) – means Full Scale nominal OD in Inches and mm for the 1:43.5 dimensions to it’s immediate right.
  • Sub-Column 3 – OD [in] (mm). This is the 1:43.5 dimensions of the pipe OD from the immediate left. The nominal size is in bold followed by the dimensions in [inches] and (mm).
  • Sub-Column 4 – Labeled FS OD [in] (mm) – means Full Scale nominal OD in Inches and mm for the 1:48 dimensions to it’s immediate right.
  • Sub-Column 5 – OD [in] (mm) This is the 1:48 dimensions of the pipe OD from the immediate left. The nominal size is in bold followed by the dimensions in [inches] and (mm).

Using #228 Evergreen tubing as an example: It is 0.250″/6,3 mm OD. I don’t care about the ID in this table ..we are concerned with what we see with our eyes. We next scan to the right to see that a nominal 10″ pipe has a 10.75″/273 mm OD. This same pipe in 1:43.5 would be 0.247/6,28 mm (looking to the next right). This means our Evergreen tubing is only over sized by 0.003″/0.08 mm. The rest of the table continues in a like fashion as this same #228 tubing could be used as 12″ pipe in 1:48 where it is ).01″/0.04mm under the nominal pipe diameter.

1:43.5 1:48
Evergreen FS OD [in] (mm) OD [in] (mm) FS OD [in] (mm) OD [in] (mm)
#223 0.093 (2.4)
#224 0.125 (3.2) 6 [0.138] (3.5)
#225 0.156 (4.0) 6.625 (168.3) 0.152 (3.87)
#227 0.219 (5.5)
#228 0.250 (6.3) 10.75 (273) 10 [0.247] (6.28)
Over 0.003 (0.008)
scale 0.348 (8.84)
12.75 (323.9) 12 [0.266] (6.75)
Under 0.016 (0.04)
scale 0.768 (19.5)
#229 0.281 (7.1) 12.75 (323.9) 12 [0.293] (7.44)
Over 0.012 (0.3)
scale 0.522 (13.3)
14 (355.6) 14 [0.292] (7.4)
Over 0.011 (0.3)
scale 0.528 (13.4)
#230 0.31 (7.9) 14 (355.6) 14 [0.322] (8.18)
#231 0.344 (8.7) 16 [0.0.333] (8.47)
Under 0.011 (0.3)
scale 0.528 (13.4)
#232 0.375 (9.5) 16 [0.368] (9.34)
#234 0.428 (11.1)
#236 0.500 (12.7)

Flange Overview

This is not meant in any way, shape or fashion to be an engineering reference. Instead it is a VERY generalized reference to enable creating reasonable facsimiles of pipe for modeling.

There are many different flange standards to be found worldwide. To allow easy functionality and interchangeability, these are designed to have standardised dimensions. Common world standards include ASA/ASME (USA), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean).

(Looks like I may have been wrong in calling flanged pipe US and/or British. Perhaps. I still need another cup of coffee to wake up this morning)

In most cases these are interchangeable as most local standards have been aligned to ISO standards, however, some local standards still differ (e.g. an ASME flange will not mate against an ISO flange). Further, many of the flanges in each standard are divided into “pressure classes”, allowing flanges to be capable of taking different pressure ratings. Again these are not generally interchangeable (e.g. an ASME 150 will not mate with an ASME 300).” 2


O scale 6″ Globe Valve

No. 6 This was the original design from way back in 2017. Honestly .. I don't know why I made it this way. With the double-flanges it shows the valve-side flange and the pipe-side flange but with a 1.58 mm hole though the body. That is a 1/16" hole so my *assumption* (I slept some...

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British O Scale 10″ Flanged Elbows

Curviloft I will be using a Sketchup plugin named Curvilot to "Create loft junctions following a given path" Take a look at the drawing to the left. You are looking at it from a side view. There are three items of interest here .. a circle representing the #228 dia at either end of a...

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Flanged Pipe

There is a sub-page to this one .. British O Scale 10"Flanged Elbows Overview I was asked by a Gentleman (name withheld unless he gives me permission to use his name) to create flanged elbows for a project he is working on. It shouldn't have been a surprise to discover that the US, UK and...

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  1. Wikipedia – Nominal Pipe Size[]
  2. Wikipedia – Flange[]

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