Is there a way to see both in one day trip? We are currently in Amsterdam and would like to try and combine seeing both windmills and tulip fields in one day trip. Any suggestions?

Apart from a few left at Keukenhof I doubt very much there are any tulips still in the fields. They were early this year and will all have been de-headed by now I would think.

You could go to Keukenhof and then on to Kinderdijk maybe or
you could go to Zaanse Schans for windmills and then up to Alkmaar which will take you through a bulb growing area, but as I say it's doubtful there are any flowers left to see.

Keukenhof closes on Friday btw.

A car would be handy for trying to find any fields still in flower.

Keukenhof's website says there are still late flowering tulips to be seen there, plus flowering rhododendrons and lots of lilies and summer bulbs.

Thanks so much hetismij! Is is feasible to do both in one day?

It would be a long day certainly. More feasible with a car than by train/bus I think. Kinderdijk is awkward to get to by public transport I believe.
Zaanse Schans is on the same railway line as Alkmaar so you could do those in one day, but I'm not sure what tulip fields, if any, you'd see from the train - I have never taken it to Alkmaar.

There is of course the windmill at Keukenhof, and there are several around that area, including 2 near Lisse, though most are not open to the public.

The Zaanse Schans is a good place to see and climb around inside a real mill. De Adriaan windmill in Haarlem is another possible and easier to get to from Amsterdam. It was rebuilt about 10 years ago so it doesn't have that "old" feel to it.