Calendly already makes QR codes, in its mobile app. Its guide has you open Event Types, pick one, tap More share options and then Create QR code, and it describes two uses: showing the code on your phone for someone to scan on the spot, or saving it to your photo album to pull up offline. That covers a conversation at a conference. A code on a desk sign, a poster or the back of a business card needs a file sized for print, and this page makes one from the same link.
Which link to use. Calendly lets you copy two kinds of link from the Scheduling page: an event type link, which books one kind of meeting, and your landing page link, which lists every active event type. Print the event type link when the sign is for one thing, such as a consultation. Never print a single-use link: Calendly says it expires once the meeting is booked, so the code would work for the first person and fail for everyone after.
Tag the link, and Calendly records where bookings came from. Calendly's help centre says it tracks UTM parameters in scheduling links: utm_source, utm_medium, utm_campaign, utm_content and utm_term. Append them to the link after a question mark, then find the bookings on Calendly's Calendar page under Filter, then Tracking IDs, and export the list as a CSV. A desk-sign code tagged utm_source=desk-sign&utm_medium=qr then tells you how many meetings it booked, which says more than a scan count. Build the tags with the UTM builder. Calendly asks for %20 for spaces and values of 255 characters or less.
Tags make the code denser. Calendly's help example, written as a full address, https://www.calendly.com/yourlink, is 33 bytes and a 29 by 29 grid. With ?utm_source=desk-sign&utm_medium=qr&utm_campaign=consults added it becomes 90 bytes and 41 by 41. A 20mm business card still holds that at error correction M, but add a logo, which raises the level to Q, and the sizing panel asks for at least 23mm. Keep tag values short on anything card-sized.
Scans versus bookings. A code that points straight at Calendly can't report its scans, to you or to any generator, and the notice under the tool says so. The UTM tags above count the bookings instead, which is the number a desk sign is there to produce. For the scan count as well, see tracking QR code scans.
Printing it. The Table tent preset, 40mm, suits a desk sign read from about 40cm, and the Poster preset, 120mm, suits a wall read from about 1.2m. QR code best practices for print has the checklist for contrast and paper finish, and the QR code reader will show whether your UTM tags made it into the finished code.