GCM有效负载大小计算php

Question

I'm sending GCM messages with payload from PHP, I would like to calculate the size (in bytes) of the array I create to use as the payload I send. This because while I'm creating it if I pass the max allowed size i want to stop and send and then continue creating a new message. On php.net I can't seem to find a function to calculate the size of an array in bytes, any ideas on how I could go about it? Thank you, James