Is a day trip to Siena worth it?

Siena is totally different from San Gimignano and Florence. I much prefer it to San G. However, will you have enough time to see Florence and it’s treasures?

We did San G and Siena in the same day from Florence (with a bus tour), so it can be done (albeit you can't spend too long in either). I liked Siena quite a bit, it is much less touristy than San G, which I also enjoyed. The gelato there is amazing! :) I think you should go to Siena, it has a very cool vibe, much smaller and less crowded than Florence. I think if we ever get to go back to Italy, I might chose Siena as a base for Tuscany.

Yes - loved it

I loved Siena too - did as a day trip from Florence. Hope to spend a night in Siena someday.

vballrains, Siena is a historic, beautiful city, with a number of things to see and do, which are not museums. I found it especially lovely in the very late afternoon and through the evening, after the day trippers have moved along. So, it would be great to spend a night or two in Siena, if possible, or at least stay through dinner and get a late bus back to Florence. San Gimignano is also beautiful, much smaller than Siena, and even more tourist-oriented, especially during the heart of the day. One key to visiting SG, I think, Is to wander beyond the principal uphill street leading up to the main piazza, so you get beyond the tourist crowds. It would be hard to give both SG and Siena justice in one single day, but to do that I would suggest going to SG first thing in the morning, move on to Siena around mid-day, and then stay through dinner. Not sure if the bus schedules, or your energy level, would make that easy or not.

Big YES and went to zero museums in Siena.
I did not get to San Gim but since I had to choose 1 as not to be rushed and think we made the right choice with Siena.

Siena is wonderful, definitely needs a full day to really enjoy it. A night or two is even better. Nothing like Florence at all.

That sounds great Im just worried that will be a lot of long bus rides that day to get to sang then to siena and then back to Florence. any advice of best way to travel this without a tour?

You will be in Florence 3 full days, but one is already taken up by a tour outside of Florence. If you take a trip to Siena, you are left with only one full day in Florence. I don't think that is nearly enough. I've been to Florence twice for 3-4 days each and have yet to reach the point of needing to take a day trip somewhere else. Pencil Siena in, but seriously think of just enjoying Florence. It is more than museums. IMO

I should have read your initial posting more carefully. If you really only have three full days in Florence and are already going out for a day trip then that should be it. I did one day trip out of eight days there. Have to agree that three days are not enough for two day trips, really not even the one.

I am in agreement with everyone else so far. The only caveat when are you traveling? As someone before wrote, Siena is hilly, lots of ups and downs. August would be tough.
I am a big believer in your first visit should give you a taste of a country/area. So, not spending more time in Florence to see San G and/or Siena seems reasonable.
All that said, you can spend months in Florence and not see it all. It is that important a world-class city. Though a lot of there there is in the museums!