How big is this bike?

Looks like it’s a Large.

The seller can’t tell you the size?

Cannondale Treadwell has two sizes.

* SM for Height – *4’11″* – *5’6″*
* LG for Height – *5’4″* – *6’0″*

When you look at the bike look for the LG or SM sticker on the frame.

Cannondale site photo looks to be a small, where the top part of the seat tube from the crossobar up looks shorter than the bottom part [https://embed.widencdn.net/img/dorelrl/w5xutg4tz2/1100px@1x/C21_C63352U_Treadwell_Neo_2_EQ_Remixte_GRY_PD.webp](https://embed.widencdn.net/img/dorelrl/w5xutg4tz2/1100px@1x/C21_C63352U_Treadwell_Neo_2_EQ_Remixte_GRY_PD.webp)

Your photo seems to be a large since the seat tube sections above and below the crossbar seem to be the same length.

More size photos..

Large [https://cyclelimited.com/products/cannondale-treadwell-neo-eq-remixte-hybrid-e-bike-2020-large](https://cyclelimited.com/products/cannondale-treadwell-neo-eq-remixte-hybrid-e-bike-2020-large)

Small [https://hips.hearstapps.com/hmg-prod/images/cannondale-treadwell-0006-1566249300.jpg](https://hips.hearstapps.com/hmg-prod/images/cannondale-treadwell-0006-1566249300.jpg)