One of my friends keeps saying she's taller than me, but I wanna measure our heights without a ruler and all, how do we measure each others height?

I was at my friends house and she keeps insisting she's taller than me but i just wanna measure our heights but non of us have a a ruler or anything like that to measure our heights, what would be the easiest way to measure each other heights and how? Also what should we be aware of?

One of my friends keeps saying she's taller than me, but I wanna measure our heights without a ruler and all, how do we measure each others height?
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