Provided is a method for determining a volume, at room temperature, of a first chamber having an unknown volume that is in fluid communication through a controllable valve with a second chamber having an unknown volume. The method can include measuring, by a pressure sensor coupled to one of the first chamber and the second chamber, a first equilibrium pressure of a gas that was introduced into the second chamber in both the first chamber and the second chamber after equilibrium is reached; measuring, by the pressure sensor, a second equilibrium pressure of the gas that was introduced into the second chamber in both the first chamber and the second chamber after equilibrium is reached, wherein the first chamber comprises an object with a known volume therein; and determining the volume of the first chamber based on the first equilibrium pressure and the second equilibrium pressure.
 This invention was made with U.S. Government support under Grant No. DE-SC0004624 awarded by the Department of Energy. The U.S. Government has certain rights in the invention.