I just had a root canal how long can i wait before putting a crown in?

Depends: You shouldn't wait longer than one month. The crown should be started as soon as possible following the treatment.

Crown over rt canal: Depends on how much natural tooth structure remains. The more natural tooth and the smaller the root canal access, the stronger the tooth. Not all teeth require a crown after a root canal. However, if a tooth has significant tooth loss due to decay, fracture, or previous large fillings, the sooner you get a crown, the less chance of losing the tooth.

ASAP: You should have the crown placed as soon as possible to protect the treated tooth. If not you risk the possibility of fracturing it and consequently loosing it.

ASAP: Get it done as soon as you can as teeth can and do crack and moreso after a root canal. If it breaks before the crown, the dentist may have to do extra proceedures to save the tooth, or you may lose it entirely and then you've wasted the money and time doing the root canal.