You can easily measure and "weigh" boulders with a few minutes of time and some basic supplies. Such measurements can be fun science experiments, make an interesting vacation fact or help you plan your landscaping project.
Determine what type of rock the boulder is formed from. You may do this by asking a park ranger, consulting your earth science guide or looking for signage close to the boulder. (In a landscaping store, this information should be readily available from the store clerk.)
Measure the boulder's length. Hold you tape measure at one end of the boulder and have a friend pull the tape out to the other end. Use your scrap paper and pencil to record the measurement.
Repeat Step 2 for height and width. Be careful measuring the height. If the boulder is tall, you may prefer to estimate that number based on a friend's height rather than climb the rock.
All dimensions need to be in feet. Since boulders aren't perfectly square, it may be easiest to simply round each dimension to the closest foot. For example, 35 inches would become 3 feet and 79 inches would be 6 feet.
Using your calculator multiple the length, width and height to determine the area of the boulder. The answer will be in cubic feet. For a boulder 3 feet long, 4 feet wide and 2 feet tall, you'd multiply 3x4x2. The area of the boulder would be 24 cubic feet.
Multiple the area you found in Step 5 by the weight per cubic foot of your rock type (see tips). For example, let's say our sample rock is made of sandstone, which weighs 150 lbs per cubic foot. The boulder would weigh 3,600 lbs. (24 cubic feet x 150 lbs per cubic foot).
Use your calculator to divide your boulder's weight by 2,000 in order to determine tons. For example, our 3,600 pound boulder is 1.8 tons.