EMT Conduit Size Table
| Trade size (US) | Metric (mm) | Weight lb/100 ft | Weight kg/100 ft | OD (in) | OD (mm) | Wall (in) | Wall (mm) |
|---|---|---|---|---|---|---|---|
| 1/2 | 16 | 30 | 13.6 | 0.706 | 17.9 | 0.042 | 1.07 |
| 3/4 | 21 | 46 | 20.9 | 0.922 | 23.4 | 0.049 | 1.25 |
| 1 | 27 | 67 | 30.4 | 1.163 | 29.5 | 0.057 | 1.45 |
| 1 1/4 | 35 | 101 | 45.8 | 1.51 | 38.4 | 0.065 | 1.65 |
| 1 1/2 | 41 | 116 | 52.6 | 1.74 | 44.2 | 0.065 | 1.65 |
| 2 | 53 | 148 | 67.1 | 2.197 | 55.8 | 0.065 | 1.65 |
| 2 1/2 | 63 | 216 | 98 | 2.875 | 73 | 0.072 | 1.83 |
| 3 | 78 | 263 | 119.3 | 3.5 | 88.9 | 0.072 | 1.83 |
| 3 1/2 | 91 | 349 | 158.3 | 4 | 101.6 | 0.083 | 2.11 |
| 4 | 103 | 393 | 178.2 | 4.5 | 114.3 | 0.083 | 2.11 |
| Type | Relative labor | Relative weight | Relative material cost |
|---|---|---|---|
| RMC (rigid steel, baseline) | 1.0 | 1.0 | 1.0 |
| Aluminum RMC | 0.89 | 0.55 | 0.99 |
| IMC (intermediate) | 0.89 | 0.76 | 0.84 |
| EMT | 0.62 | 0.42 | 0.35 |
| PVC | 0.55 | 0.20 | 0.43 |
Electrical metallic tubing (EMT) is the thin-walled steel conduit that carries most exposed wiring in modern North American buildings, and its sizing system hides a trap on every label: trade size is a name, not a measurement. Half-inch EMT actually measures 0.706 inches across, and its metric designator - 16, for the roughly 16 mm metric equivalent - is its own rounding. The chart below gives the whole trade-size ladder from 1/2 to 4 with the real outside diameters, wall thicknesses and weights electricians quote from.
The other half of conduit selection is what the table cannot show: wire fill. Code limits how many conductors go inside any conduit by cross-sectional area, so a 1/2-inch EMT run may legally hold only a few #12 wires while the same tube swallows dozens of small control wires - the conduit is a chute, and the fill table, not the trade size, sets the ceiling. Material choice follows the environment: EMT for dry indoor exposure, PVC for buried or wet runs, and thick-walled rigid metal (RMC) where physical damage is the design case.
How to use
- Order by trade size, verify by outside diameter: the names 1/2, 3/4, 1 are inherited plumbing-style labels, so when a fitting list says 0.706 or 0.922 OD, match the chart - couplings and connectors are toleranced to the real number, not the nickname.
- Convert for the metric world: the metric designator column (16, 21, 27, 35, 41, 53, 63, 78, 91, 103) is the trade size translated to nominal millimeters, and international drawings use it directly - a spec calling for size 27 conduit is asking for 1-inch EMT.
- Budget by weight and labor: EMT wins installations on weight (30 pounds per 100 feet at 1/2 inch, light enough for one-hand work) and on tool-made, non-threaded joints; compare materials with the relative-cost table before committing a long run to rigid steel.
Frequently asked questions
What is the outside diameter of 1/2-inch EMT?
0.706 inches (17.9 mm), with a 0.042-inch wall - nothing about half-inch EMT actually measures half an inch. The trade size is a legacy label from the days when conduit sizing followed iron pipe conventions, and the metric designator 16 rounds the outside diameter down to a nominal 16 mm. That gap is why fitters buy fittings by trade size but cut, bend and thread to the chart values: a saddle bend keyed to the assumed half inch comes out visibly wrong on the wall.
Is EMT the same as rigid conduit?
No - the wall thickness is the whole story. EMT is the thinnest of the steel raceways (0.042 to 0.083 inches across this chart), bent with a hand tool and joined with compression or set-screw fittings that grip, not threads. Rigid metal conduit (RMC) has a wall several times thicker, can be threaded in the field, and earns its weight where physical damage is plausible - along a loading dock, through a parking structure. EMT is the default for finished indoor spaces precisely because it is cheap, light and fast; it is not a smaller RMC.
How many wires fit in a conduit?
That is a wire-fill question, not a conduit-size question, and the answer lives in the code's fill tables rather than this chart. Fill is capped by the percentage of the conduit's internal cross-sectional area that conductors may occupy - roughly 40 percent for three or more wires - so the limit depends on wire size, insulation type and count together. One #12 THHN slides through 1/2-inch EMT easily; a dozen do not. Oversizing one trade size is usually cheaper than a failed inspection, and the chart above gives the inside diameter through the wall thickness column to run the math.
Why does metric EMT sizing not match inches exactly?
Because each system rounds to its own convenient number. Trade size 3/4 has a 0.922-inch outside diameter (23.4 mm), and its metric designator is 21 - neither 23.4 nor 0.922 appears in the other system. The metric designators follow the ISO preference for nominal series (16, 21, 27, 35, 41, 53, 63, 78, 91, 103), chosen for catalogue tidiness over dimensional truth. Treat the two columns as parallel names for the same physical tube and keep the OD column as the only number a caliper would confirm.