A planar volumetric device for quantifying and handling a body fluid sample is provided. The device has a planar main body, a body fluid sample flow path, an air pump and an air passage. The planar main body includes a first planar surface and a second planar surface. The body fluid sample flow path is disposed in the main body, and has a body fluid sample inlet, a middle junction and a body fluid sample outlet, wherein the middle junction and the body fluid sample outlet define therebetween a specific path segment, by which it is possible to externally observe to which extent the body fluid sample has filled up with the path segment. The air pump is configured to provide an operating air pressure. The air passage has a first end and a second end, wherein the first and the second ends are connected to the air pump and the middle junction respectively, and the specific path segment has a constant volume.