This is the official Davidian Height Chart for official Davidian Referenced Character Heights, or ODHCFIDRCH for short Please ask if you want your character to be added :D
By using David as a scale of 5 ft (which is canon to BFDI), and by measuring the amount of pixels tall he is, which is 360, and dividing by 5, you get 72 pixels per foot. If you take another character, like Lantern, who is 270 pixels tall, and divide by 72, you get a measurement of 3.75, or 3' 9" tall.