The volumes of regular geometric shapes, such as cubes or cylinders, are usually determined by applying a geometric equation. The volume of a cube, for instance, is determined by multiplying the cube's height by the length and width of one of the sides, while the volume of a cylinder is calculated by multiplying the height of the cylinder by pi (approximately 3.14) and the radius of the circular side squared. Simply measure the necessary attributes of the geometric object and apply the appropriate formula, available from a basic geometric reference. Sometimes, irregular geometric objects, like a sphere over a cylindrical shaft, can be divided into component parts in order to calculate the volume of each part and then add the parts together to calculate total volume.
One of the most common techniques for measuring the volume of irregular solid objects, displacement involves the submersion of a solid in a measured container of liquid. The increase in the level of the liquid after the solid has been introduced is equivalent to the volume of the solid. By submerging several coins in a graduated cylinder of water, for example, you can measure the change in the water level and use that measurement to determine the volume of the coins.
The fact that liquids adjust to the shape of the object that contains them makes measuring their volume particularly easy with basic laboratory equipment. Using a graduated cylinder, a cylindrical instrument with volume markings along one side, or a buret, a graduated pipe used to dispense liquids in certain volumes, you can simply fill these tools with a certain amount of liquid, allow the liquid to sit on an even surface and measure its volume by seeing what volume marking coincides with the top surface of the liquid in the container. Remember that the top of a liquid surface will never be completely flat, rather curve up or down depending on the viscosity of the liquid, so take your measurement from the lowest level of the top surface to approximate the best measurement.
While gasses, like liquids or solids, have a certain volume or amount of space they occupy, the volume of gasses depends heavily on the amount of pressure and temperature applied to the gas. This same phenomenon can be observed in liquids and solids, but the effects are much more pronounced on gasses. As a result, measurements of gas volumes usually include a clarification of the temperature and pressure conditions at the time of measurement. "Standard Conditions", a convention specifying zero degrees Celsius and one atmosphere of pressure are frequently used for measuring the volume of gasses. Otherwise, gasses can be measured much like liquids, using a graduated syringe to take in a certain volume of gas.