Yes there is a device called a nose-weight gauge. I use an old set of bathroom scales and a piece of wood placed under the tow hitch and then wind the jockey wheel up so the weight is on the wood and so gives me the nose weight usually 70kgs. Hope this helps.
If you go for the bathroom scales option, make sure the piece of wood on the scales ends up being the same height as the tow ball on your car. This should give you the most accurate readings. Also make sure the weight is spread across the scales using another piece of wood.
I am not Quite as tecnical as most of the others as I walk to the front and if I can just lift the jockeywheel off the ground with a real strugle it is right it has worked with trailers for in excess of 15 years and seems to work with the caravan it tows fine without any stabaliser.
Cheap noseweight gauges are rubbish though, Pete's suggestion is as good providing you can physically lift that weight.
Get a calibrated noseweight gauge. Or get a set of accurate scales and put a thick board on them to spread
the weight. Then use a stick that measures the same height whilst on the scales as your towball on the car.
So a 15" towball height your stick needs to be 12" - the thickness of teh scales and board.
Make sure you use the board. I didnt and broke the scales. Wife was not happy. Had to buy her a new one.