The best tenkara line length can vary depending on various factors, including the type of fishing you plan to do, the size of the stream or river you'll be fishing in, and your personal preferences. In general, your line should be the same as your rod length. If fishing in smaller streams or areas where there are lots of overhanging trees, a shorter line is beneficial. On larger rivers or when longer casts are required, a long rod and longer line are advantageous as it allows for better reach and the ability to cover a larger area.