The weight of any object is simply the force of gravitational acceleration scaled by the mass of the object. Since the acceleration due to gravity is constant over the surface of the Earth, all that is generally required to calculate the weight of any specific element or compound is its density. This linear proportionality suggests that the only dependent variable in calculating the weight of aluminum is the volume of the object.

Write down the density of aluminum. Aluminum is a base element with a well-documented density. The density of aluminum, or dAl, is about 2.7 grams of mass per cubic centimeter of volume. Therefore, dAl = 2.7 g/cm^3.

Determine the volume of the aluminum whose weight you wish you calculate. The volume can be determined by measuring the length, width and height of the piece of aluminum whose weight is to be calculated. You can use a ruler for this task. The volume V is simply the product of all three lengthwise measurements: V = l x w x h where l is the length, w is the width and h is the height.

Multiply the density of aluminum by the measured volume. This will result in a calculation of the overall mass of the aluminum sample: dAl x V = mAl where mAl is the mass.

Multiply the mass of the aluminum by the Earth's gravitational acceleration. Weight is a measure of force, a quantity that requires a factor of acceleration. The gravitational acceleration on the surface of the Earth is a well-documented constant at 9.8 m/s^2 where m/s^2 stands for "meters per second squared." The units utilized herein will render a weight measurement in SI units of Newtons, or gram meters per squared seconds (g x m/s^2).