# Rigid (RMC), IMC and EMT conduit sizes to 4 in: outside diameter, wall and inside diameter by trade size, inches and mm

> What is the outside diameter of 1/2 inch rigid conduit, IMC, and 3 inch EMT?

- Category: Tri-clamp & pipe › Pipe, tube & threads
- Kind: Standard part
- Basis: Wheatland Tube (RMC OD and ID), BIA conduit catalog (walls, EMT 2-1/2 to 4), Allied Tube IMC cut sheet; numbers only, disagreements shown
- Page: https://xemstudio.com/objects/rigid-imc-emt-conduit-sizes-to-4-in/ · JSON: https://xemstudio.com/api/geometry?object=rigid-imc-emt-conduit-sizes-to-4-in · Plain text: https://xemstudio.com/objects/rigid-imc-emt-conduit-sizes-to-4-in/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
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**Exact dimensions.** Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part.

## Notes

- Rigid metal conduit (RMC, also called GRC, galvanized rigid conduit): OD and ID by trade size from Wheatland Tube's submittal sheet (ANSI C80.1, UL 6; its OD tolerance is ±0.015 in for 1/2 to 1-1/2 in and ±1% for 2 in and up); walls from BIA's conduit page. BIA prints the rigid OD rounded to 0.1 in (0.8, 1.0, 1.3 ...) so its OD is not used; Wheatland's nominal ID agrees with BIA's wall on every row (OD − ID = 2 × wall to 0.0015 in).
- IMC (intermediate metal conduit, ANSI C80.6): Allied Tube's cut sheet gives OD and wall; BIA's catalog page prints a thicker wall for every size (for 1/2 in: Allied 0.070 in, BIA 0.078 in; for 4 in: 0.140 and 0.150), so both are shown and the ID is computed from Allied's wall. Check the maker's sheet for the one you buy. BIA's rounded IMC OD is not used.
- EMT sizes 1/2 to 2 in are on the emt-conduit page (OD 0.706 to 2.197 in); this page adds 2-1/2 to 4 in from BIA's conduit page (ANSI C80.3): the wall is printed there and the ID is computed. Only one source was read for them. BIA's EMT values for 1/2 to 2 in agree with the emt-conduit page.
- Trade size (and the metric designator 16 to 155) identifies the size; per the Steel Tube Institute 'they are for identification purposes only and are not actual dimensions'. Knockout diameters for the same trade sizes are on the knockout page.
- Left out: thread dimensions and lengths of rigid and IMC (the threads are NPT-style conduit threads with their own lengths), bend radii, coupling and fitting dimensions: the set-screw EMT connector and coupling sheets read (EMCO ERI, O-Z/Gedney) print drawing dimensions as A, B, C without saying which each is, so none is tabulated. No files: a conduit stick is a plain tube; the OD and wall are the numbers.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| rigid conduit OD | 1/2: 21.34, 3/4: 26.67, 1: 33.40, 2: 60.33 | knockout of the same trade size (Ø22.225, Ø28.17, Ø34.925, Ø62.71 nominal) | designed | all |
| IMC OD | 1/2: 20.70, 3/4: 26.13, 1: 32.76 | knockout of the same trade size | designed | all |

## Sizes

| type | trade size (in) | metric designator | OD (in) | OD (mm) | wall (in) | wall, second source (in) | ID (in) |
|---|---|---|---|---|---|---|---|
| rigid (RMC / GRC, ANSI C80.1) | 1/2 | 16 | 0.840 | 21.34 | 0.104 | - | 0.632 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 3/4 | 21 | 1.050 | 26.67 | 0.107 | - | 0.836 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 1 | 27 | 1.315 | 33.40 | 0.126 | - | 1.063 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 1-1/4 | 35 | 1.660 | 42.16 | 0.133 | - | 1.394 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 1-1/2 | 41 | 1.900 | 48.26 | 0.138 | - | 1.624 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 2 | 53 | 2.375 | 60.33 | 0.146 | - | 2.083 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 2-1/2 | 63 | 2.875 | 73.03 | 0.193 | - | 2.489 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 3 | 78 | 3.500 | 88.90 | 0.205 | - | 3.090 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 3-1/2 | 91 | 4.000 | 101.60 | 0.215 | - | 3.570 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 4 | 103 | 4.500 | 114.30 | 0.225 | - | 4.050 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 5 | 129 | 5.563 | 141.30 | 0.245 | - | 5.073 (printed) |
| rigid (RMC / GRC, ANSI C80.1) | 6 | 155 | 6.625 | 168.28 | 0.266 | - | 6.093 (printed) |
| IMC (ANSI C80.6) | 1/2 | 16 | 0.815 | 20.70 | 0.070 (Allied) | 0.078 (BIA) | 0.675 (computed, Allied wall) |
| IMC (ANSI C80.6) | 3/4 | 21 | 1.029 | 26.13 | 0.075 (Allied) | 0.083 (BIA) | 0.879 (computed, Allied wall) |
| IMC (ANSI C80.6) | 1 | 27 | 1.290 | 32.76 | 0.085 (Allied) | 0.093 (BIA) | 1.120 (computed, Allied wall) |
| IMC (ANSI C80.6) | 1-1/4 | 35 | 1.638 | 41.60 | 0.085 (Allied) | 0.095 (BIA) | 1.468 (computed, Allied wall) |
| IMC (ANSI C80.6) | 1-1/2 | 41 | 1.883 | 47.82 | 0.090 (Allied) | 0.100 (BIA) | 1.703 (computed, Allied wall) |
| IMC (ANSI C80.6) | 2 | 53 | 2.360 | 59.94 | 0.095 (Allied) | 0.105 (BIA) | 2.170 (computed, Allied wall) |
| IMC (ANSI C80.6) | 2-1/2 | 63 | 2.857 | 72.56 | 0.140 (Allied) | 0.150 (BIA) | 2.577 (computed, Allied wall) |
| IMC (ANSI C80.6) | 3 | 78 | 3.476 | 88.29 | 0.140 (Allied) | 0.150 (BIA) | 3.196 (computed, Allied wall) |
| IMC (ANSI C80.6) | 3-1/2 | 91 | 3.971 | 100.86 | 0.140 (Allied) | 0.150 (BIA) | 3.691 (computed, Allied wall) |
| IMC (ANSI C80.6) | 4 | 103 | 4.466 | 113.43 | 0.140 (Allied) | 0.150 (BIA) | 4.186 (computed, Allied wall) |
| EMT (ANSI C80.3), sizes above the emt-conduit page | 2-1/2 | 63 | 2.875 | 73.00 | 0.072 (BIA) | - | 2.731 (computed) |
| EMT (ANSI C80.3), sizes above the emt-conduit page | 3 | 78 | 3.500 | 88.90 | 0.072 (BIA) | - | 3.356 (computed) |
| EMT (ANSI C80.3), sizes above the emt-conduit page | 3-1/2 | 91 | 4.000 | 101.60 | 0.083 (BIA) | - | 3.834 (computed) |
| EMT (ANSI C80.3), sizes above the emt-conduit page | 4 | 103 | 4.500 | 114.30 | 0.083 (BIA) | - | 4.334 (computed) |

## Where the files are

- Wheatland Tube: [Rigid Metal Conduit submittal sheet (Canada, English): nominal OD and ID by trade size 1/2 to 6, ANSI C80.1, UL 6](https://www.wheatland.com/wp-content/uploads/2022/05/Rigid-Metal-Conduit-Submittal-Sheet-–-Canada-English.pdf) — web — Publisher's page; dimensions are facts
- BIA (biaonline.com): [Conduit catalog page 7201: GRC (ANSI C80.1), IMC (ANSI C80.6) and EMT (ANSI C80.3) OD, wall by trade size (OD of GRC and IMC printed rounded to 0.1 in)](https://www.biaonline.com/catalog/pdfs/72/7201.pdf) — web — Publisher's page; dimensions are facts
- Allied Tube & Conduit (utilitypipesupply.com copy): [IMC cut sheet: OD and wall by trade size 1/2 to 4 (ANSI C80.6, UL 1242)](https://utilitypipesupply.com/cdn/shop/files/Allied_Tube_Conduit_IMC_Cut_Sheet.pdf) — web — Publisher's page; dimensions are facts
- Steel Tube Institute: [Steel conduit and EMT metric designators (trade sizes are for identification, not actual dimensions)](https://steeltubeinstitute.org/faq/steel-conduit-emt-metric-designators/) — web — Publisher's page; dimensions are facts

## Questions

**What is the OD of 1/2 inch rigid conduit?**

0.840 in (21.34 mm), 0.104 in wall, 0.632 in ID (Wheatland); the same OD as NPS 1/2 pipe.

**What is the OD of 3/4 inch IMC?**

1.029 in (26.13 mm) per Allied Tube; wall 0.075 in (Allied) or 0.083 in (BIA).

**What is the OD of 3 inch EMT?**

3.500 in (88.9 mm), 0.072 in wall (BIA).

**What does metric designator 21 mean?**

It identifies 3/4 in trade size (identification only, not a dimension).

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