iOS: Last week we saw a cool app that turned the 3D Touch feature on the iPhone 6s into a scale, but Apple pulled the app. Thankfully, one place Apple can't pull an app from is the internet, which is why a web app is a perfectly suitable replacement. From your iPhone 6s, head to this web site on GitHub, place a spoon on top of the screen, tap the Tare button to zero out the scale, and place your object on the spoon. You'll then get the weight in grams. As you'd expect, it's not super accurate, but it does work in pinch.
Scale [GitHub via OS X Daily]