LTE-M(CAT-M1) bandwidth in T-Mobile

That would depend on location and how much is allocated for.LTE.vs. 3g, 2g or 5g.

Eg.  LA county has 15x15 B2, 20x20 B4, 5x5 B12, 10x10 B71, and 40MHz for B41

And

5MHz B2 UMTS/GSM

15x15 MHz n71 5g

100MHZ  n41 5g

Other locations have different allocation based on MTA/BTA licenses.

I’m not aware of which is used for lte-m  you'll be more likely to find low power 5g

drnewcomb and formercanuck are partially correct, but don’t answer the orginal question.

• Cat-M1 uses 1.4MHz channel bandwidth, fixed in the 3GPP spec
• Not every LTE band a carrier offers can use Cat-M1, as carriers only use a specific subset of their LTE bands for use with this AT (Access Technology).  For example:
  • AT&T publicly documents it uses these LTE bands: 2, 4, 5, 12, 14, 17, 29, 30, 66 and the LTE-M bands supported are only 2, 4, 12

I’m on the phone with T-Mobile support now to get some truth about which LTE-M bands are in use in North America.  They have responded that they only have this map available to spot check a specific address...which doesn’t answer the much desired question, but does show if you expand the details that band 12 is used for LTE-M (Cat-M1). 

It’s common that a carrier will only use a single band and that single band be a low frequency band so the IoT device has the best chance possible to reach home out of difficult cellular situations.