Not as far as I know unfortunately. At least not an accurate one.
The only one I know about is http://fishweights.net but its now a paid for application and doubt it will be accurate as males and females differ massively in length and girth. And even same sex same length can differ by as much as 30%
I would suggest posting a Pic and ask for an honest opinion but the amount of idiots behind keyboards this will be hard plus a photo is never a good way of seeing what size a fish really is.
My suggestion is enjoy the memory of the fish and don't worry too much about the actual weight because 50% of the people will tell you the fish only weighs 12-15kg's.
Just my suggestion.