Ethernet cable length checker.

Ethernet Cable Length Limit Checker: how it works

An Ethernet channel is the whole path between two active devices. For copper Cat 5e, Cat 6 and Cat 6A, Wikipedia's Structured cabling article gives a maximum of 90 m for the permanent link plus an allowance of 10 m of patch cords in total at the ends, which makes 100 m. The Category 6 cable article repeats the same 90 m plus 10 m split for 10/100/1000BASE-T. 100BASE-TX and 1000BASE-T specify a maximum of 100 m (Ethernet over twisted pair), and 2.5GBASE-T and 5GBASE-T can be deployed up to 100 m on Cat 5e or better (2.5GBASE-T and 5GBASE-T article).

At 10 Gbps the limit depends on the cable. The Category 6 cable article says Cat 6 is reduced to a maximum of 55 m for 10GBASE-T while Cat 6A allows 100 m, and the same article lists a reference noting a 37 m figure from TIA TSB-155 against IEEE's 55 m, so treat anything past 37 m on Cat 6 at 10 Gbps as needing a test. The Category 5 cable article quotes a switch datasheet saying 10GBASE-T over Cat 5e is not specified in the standard and cannot be guaranteed.

Worked example. Cat 6 at 10 Gbps with a 45 m permanent link and 5 m of patch cords is 50 m, under the 55 m limit, so 5 m of margin. A 70 m permanent link on the same cable is over the limit and needs Cat 6A.