The frame number encodes shaft height. First two digits divided by 4 gives you the D dimension in inches. Use the tables below for exact dimensions and IEC cross-reference. Do not assume IEC "equivalents" are bolt-for-bolt swaps.
How to decode any NEMA frame number
The formula works for every three-digit T-frame: take the first two digits, divide by 4. That's your shaft centerline height in inches.
143T? First two digits are 14. Divide by 4. You get 3.5 inches. Check any manufacturer's dimension chart and you'll find D = 3.5 in.
254T? First two digits are 25. Divide by 4. You get 6.25 inches. The Nidec US Motors Dimension Guide confirms it.
This trick fails on legacy frames. Frames 42, 48, and 56 predate T-frame standardization. They don't follow the formula. Look them up.
The suffix letters matter too. T means standard shaft length. TS is short shaft. C means C-face flange mount. TC combines both: C-face with the T shaft configuration. Z, Y, or any unfamiliar letter means special application. Don't auto-populate dimensions for those.
Full NEMA T-frame dimensions
This table covers the frames you'll actually encounter in MRO catalogs. Data sourced from Regal Rexnord, Marathon Electric, and Nidec US Motors published dimension guides.
| Frame | D (in) | U (in) | E × 2F (in) | Typical HP (4-pole) |
|---|---|---|---|---|
| 42 | 2.625 | 3/8 | 1.75 × 1.69 | 1/20–1/8 |
| 48 | 3.0 | 1/2 | 2.125 × 2.75 | 1/8–3/4 |
| 56/56H | 3.5 | 5/8 | 2.44 × 3.0 | 1/4–1.5 |
| 143T | 3.5 | 7/8 | 2.75 × 4.0 | 1–1.5 |
| 145T | 3.5 | 7/8 | 2.75 × 5.0 | 1.5–2 |
| 182T | 4.5 | 1-1/8 | 3.75 × 4.5 | 2–3 |
| 184T | 4.5 | 1-1/8 | 3.75 × 5.5 | 3–5 |
| 213T | 5.25 | 1-3/8 | 4.25 × 5.5 | 5–7.5 |
| 215T | 5.25 | 1-3/8 | 4.25 × 7.0 | 7.5–10 |
| 254T | 6.25 | 1-5/8 | 5.0 × 6.25 | 10–15 |
| 256T | 6.25 | 1-5/8 | 5.0 × 8.25 | 15 |
| 284T | 7.0 | 1-7/8 | 5.5 × 7.0 | 15–20 |
| 286T | 7.0 | 1-7/8 | 5.5 × 9.5 | 20–25 |
| 324T | 8.0 | 2-1/8 | 6.25 × 8.0 | 25–30 |
| 326T | 8.0 | 2-1/8 | 6.25 × 10.5 | 30–40 |
| 364T | 9.0 | 2-3/8 | 7.0 × 9.0 | 40–50 |
| 365T | 9.0 | 2-3/8 | 7.0 × 11.25 | 50 |
| 404T | 10.0 | 2-7/8 | 8.0 × 10.0 | 50–60 |
| 405T | 10.0 | 2-7/8 | 8.0 × 12.25 | 60–75 |
| 444T | 11.0 | 3-3/8 | 9.0 × 11.0 | 75–100 |
| 445T | 11.0 | 3-3/8 | 9.0 × 14.5 | 100 |
| 449T | 11.0 | 3-3/8 | 9.0 × 16.5 | 125–150 |
HP ranges are baselines for 4-pole TEFC motors at 1800 RPM. A 182T at 3600 RPM can carry higher horsepower than the same frame at 1800.
C-face bolt data
C-face motors mount differently. You need the bolt circle diameter (AJ) and the lip OD (AK). These dimensions are from Nidec and Castellano Motors published specs.
| Frame | AJ bolt circle (in) | AK lip OD (in) | Shaft U (in) |
|---|---|---|---|
| 56C | 4.5 | 5.875 | 5/8 |
| 143TC/145TC | 5.875 | 4.5 | 7/8 |
| 182TC/184TC | 7.25 | 6.0 | 1-3/8 |
| 213TC/215TC | 8.5 | 7.0 | 1-5/8 |
| 254TC/256TC | 10.0 | 8.5 | 1-7/8 |
Notice the shaft diameter. A 182TC has a 1-3/8 in shaft. A 182T has a 1-1/8 in shaft. Same base frame, different shaft. This trips people up constantly.
A catalog record that says "182T" without the C suffix is incomplete for pump applications. The shaft diameter governs coupling selection.
NEMA to IEC cross-reference
This is where replacement orders go wrong. IEC 112 and NEMA 182T get called "equivalent" everywhere. They're close. They're not the same.
| NEMA Frame | IEC Frame | NEMA D (in) | IEC H (mm) | Notes |
|---|---|---|---|---|
| 56 | 90 | 3.5 | 90 | IEC shaft smaller (24mm vs 5/8 in) |
| 143T/145T | 100/112 | 3.5 | 100/112 | Bolt patterns differ |
| 182T/184T | 112/132 | 4.5 | 112/132 | 182T is 114.3mm vs IEC 112's 112mm |
| 213T/215T | 132 | 5.25 | 132 | NEMA shaft is larger |
| 254T/256T | 160 | 6.25 | 160 | Bolt circle mismatch |
| 284T/286T | 180 | 7.0 | 180 | Not interchangeable |
| 324T/326T | 200 | 8.0 | 200 | Adapter plate required |
IEC frame numbers equal shaft height in millimeters directly. IEC 112 means 112mm shaft height. NEMA's 182T has a 4.5 in shaft height, which converts to 114.3mm. That 2.3mm difference sounds small until you're shimming a motor at 2am.
Catalog says "IEC 112 equivalent"
- Frame: 182T
- IEC equivalent: 112
- Shaft height: blank
- Swap notes: "Direct replacement"
After review
- Frame: 182T
- IEC equivalent: 112 (not direct swap)
- NEMA shaft height: 114.3mm
- IEC shaft height: 112mm
- Swap notes: "Requires adapter plate; shaft diameter differs"
The WEG NEMA Standard Dimensions poster and ESR Motors comparison chart both list these as equivalents. But NEMA shaft diameters run larger than IEC at the same frame class. Bolt patterns also diverge. Calling them equivalent without noting the delta is how you end up with a motor that doesn't fit.
Using this in catalog ops
Most motor records in distributor catalogs have the frame field populated. The dimension fields are blank. This is fixable.
A classifier can auto-populate D, U, and E×2F from the frame number using the decode formula plus a lookup table. The logic is deterministic for standard T-frame suffixes. Run the batch, then queue the edge cases for manual review.
Three-digit frame, T suffix: use decode formula, verify U from lookup table, auto-populate. Frame has C or TC suffix: check AJ/AK separately, note that shaft U is larger than foot-mount version. IEC frame listed as NEMA equivalent: flag the record, add shaft height delta in mm before marking it a match. Frame suffix is Z, Y, or unfamiliar letter: do not auto-populate, flag for manual review.
The common trap is treating IEC equivalents as interchangeable. Your feed might list "IEC 112" as a valid substitute for a 182T. It isn't. The shaft height is within 2mm but the shaft diameter and bolt pattern are different. A classifier should flag these for human confirmation, not auto-approve them.
Incoming catalog record
| SKU | Frame | D | U | E×2F |
|---|---|---|---|---|
| MTR-182T-5HP | 182T | — | — | — |
After enrichment
| SKU | Frame | D | U | E×2F |
|---|---|---|---|---|
| MTR-182T-5HP | 182T | 4.5 in | 1-1/8 in | 3.75 × 4.5 in |
The decode formula handles most of your volume. The lookup table catches the legacy frames and confirms shaft diameters. Human review catches the Z-suffix specials and the IEC swap traps. That workflow clears a backlog of incomplete motor records in a day instead of a month.