The most accurate way to determine your Koi's weight is to actually weigh it. Sometimes this is not practical, so you can use the chart below to estimate weight vs. length for a normal build Koi. Length is from tip of nose to tip of tail. Keep in mind that this table is for typical Koi. Along with knowing how much your Koi weigh now, you may want to predict how much they will weigh in the future.
Growth rates vary greatly.
The normal pond rate assumes that the Koi are fed twice a day in warm weather, less in the spring and fall, and none in winter. The low growth scenario assumes that the Koi are fed a little every few days in summer.