Translating leg and height measurements to surf ski dimensions

Hi All,
I attempting to find a system that translates my inner leg and height measurement to fit the pedal to seat length of a surf ski. I've looked around the web for awhile now without success
For example my inner leg is approximately 80 cm and my height is approximately 180 cm.
Now to translate those measurements to a surf ski, I guess part of it is measuring from the pedals to the back of the seat well.
However, I'm unsure what this measurement means, ie, how do they translate back to my body measurements? Does it need to equal my inner leg (of 80 cm)? 
I've had a surf ski in the past and eventually lost interest as it was too short in the sitting position: I don't want to make the same mistake! 
I'm looking around for a 2nd hand ski, just need a system to ask the ski's vendor to measure the ski for an approximate sizing for a visit.
I hope all this all makes sense, please let me know otherwise.
Many thanks and regards
 

Hey Andrew,

I have a suspicion that it's a long time since you first tried a surfski?  Back in the day the leg length was fixed, so it was important to know what an individual ski's cockpit length had been set to - but all skis these days have adjustable footplates that you can set to whatever length you need.

At 180, you're about my height, which is pretty much in the middle of the adjustment range on most skis.

So you should be just fine. 

Cheers,
Rob

Thanks for that Rob, very much appreciated. Understood regarding adjustable footplates, I've spotted a few on the web
However, some of the second hand ones are still fixed.
I found this short youtube that gave an indication of how to measure the leg length to the ski: 

I'm unsure if this methodology is suitable or if you have any comment.
Thanks again for all your help.
Regards

That looks as good as any other way of estimating it.  To be honest it's been so long now since I sat in a fixed-length boat...  I know I used to be a "size 5" in custom kayaks boats - but that was about 15 years ago!

I'd still strongly recommend finding an adjustable boat if you can though - aside from the benefit of being able to adjust to fit your length perfectly, the "hump" between your bum and heels tends to be a lot lower in single-footwell boats, and hence a lot more comfortable.

Good luck!

Thanks again Rob, your advice is very much appreciated. 
I'll keep a look out for adjustable skis.
Many thanks and regards,
Andrew