How much bandwidth does a T1 typically give?

By definition, a T1 provides 1.544 Mbps, full duplex. (The equivalent European specification is the E1, which provides 2.048 Mbps.)

However, it is divided into 24 channels, and they can be aggregated in any number, so you can get a "partial" T1 in many different bandwidths.

And sometimes multiple T1s are sold aggregated together in what tends to be called "bonded" T1s.

Also, sometimes "T1" is used incorrectly to mean a full-duplex business-class (which usually means "better bandwidth guarantee") circuit, or possibly even something else. You need to make sure what you're getting from your vendor.

According to Wikipedia T1 provides 1.544 Mbits/s of bandwidth both directions.

A T1 is a data circuit with 24 channels. Depending on the provisioning, it can provide different bandwidths and you won't get the full 1.544Mbps for your use. B8ZS/ESF "clear channel" uses 64k channels while AMI/D4 uses 56k channels (8k is used for control). Sometimes you'll use fewer channels, such as a fractional T1.

• 24*64k = 1.536 Mbps (slightly less due to signaling codes)
• 24*56k = 1.344 Mbps

A lot of T1s are now HDSL circuits and use a single pair instead of two pair.

Other things also use T1s like a PRI circuit. For a PRI, you often see 23 B channels to carry calls or data and 1 D channel for control.