There is a way to measure something that is longer than a ruler you have, and it is (very) portable. Mitchell Charity has a page with template on business cards, which help you measure distance and size of an object. Depends on your eye and the arm’s length and print out the appropriate pdf template that specific to the length. Then you basically hold the card at your full arm’s length and use the meter on the side to measure:

Example usage: Hold the card at arm’s length, looking past it at a distant door. Tall people, and doors, are about 2 meters (yards) tall. If a distant door comes up to the x30 mark on the card, then then it is 2 times 30 meters away, so 60 meters. If it only comes up to the x50 mark, then it would be 2 x 50 = 100 meters away. Same with tall people. A short 1 meter (3 ft) person at x50 would be 1 x 50 = 50 meters away. A 3 or 4 meter high building floor at x20 would be (3 or 4) x 20 = (60 or 80) meters away.

Angle Cards – A “business card” for measuring angle – [Mitchell Charity]