Have the ability to display % based measurements.
In mobile designs that need to be responsive, developers ask for how wide an element should be relative to the parent container.
Also, for specific platforms, it would be great to have the ability to change the value for width or height (depending upon the circumstance) to a relative value or plain text.
As an example use case, an element might have a static height (expressed as dp) while having a relative width (expressed as "Match Parent"). This would more clearly express how a a design would scale for various device widths on the Android platform.
+1 I was pretty surprised to see this doesn't exist in Zeplin yet. Relative size measurements are a must have!
Lála Ibildayeva commented
Developing an adaptive web product that is supposed to work on screen from 9" till infinity. px values just don't cut it for me.
Christopher Stumph commented
+1 Also would love to see measurements available in em's from a base font-size setting.