When building your own antennas, you can either look up a design or dimensions online or from book, or you can use a common formula. 468/MHz is commonly used to calculate the total length of a wire dipole in feet. I had a few dimensions jotted down for reference, but it’s easy to stick the formula into a spreadsheet and just enter the freqs you’re interested in. For example, here’s a Google Doc with the common HF bands:
I hope I’ve got these right, but if not, drop me a comment below.
Here’s a link direct to the Google Sheet if you’d like to bookmark it: https://docs.google.com/spreadsheets/d/1d3Mmnyzvj8AG1lFPd59RSMJhE9ihbE2M4w5noDzyedo/edit?usp=sharing