Question-and-Answer Resource for the Building Energy Modeling Community
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This answer assumes that n50 is the same as ACH50. ACH50 is the number of air changes that occur when the building is pressurized to 50 Pascals. This is a pretty common measurement in residential buildings, where a blower door is used to do the pressurization. This article gives a pretty good backstory about ACH50 and what reasonable and unreasonable values are.
Anyhow, your building probably isn't pressurized nearly that high, so you need some way to convert from whatever pressure your ACH value assumes to 50 Pa. This paper has some equations (and assumptions) that you can use. Of course, read about the assumptions and the equations to make sure you understand them before using them.
