Abstract: Portable devices for measuring the density of liquids are described. In each of these, a floating element and a reference element are pivotally mounted on a horizontal axis, the floating element being in a casing containing the liquid and having a transparency through which the floating element can be viewed. The reference element may be either outside or inside the casing and is arranged so that the gravitational force, or combined gravitational and buoyant forces thereon, maintain it in stable equilibrium about the axis, and so in a fixed position in a vertical plane irrespectively of the position of the casing in that plane. In one example the floating element is marked with a scale and the reference element is an indicator arm also immersed in the liquid and balanced by an extension on the opposite side of the axis. In another example the floating element is an indicator arm and the reference element a pendulum member marked with a scale.