The ultimate source for estimation of landing distances is the serial number matched POH of the aircraft in question.
There are some rule of thumbs around, but they are just that - bare minimum estimates with no legal or reality binding claims I know off. Each aircraft will be different and the POH will give an idea how, but not be the last answer. Especially grass take offs are often pilot guts feeling skills, as grass usually does not follow aviation standardization rules, it is a natural growing commodity with no sense for regulations. Let it be 75% humidity at take off and it will behave different to the time you landed at 65% ...
Last edited by ChickenHouse; 14th Jan 2017 at 09:37.