♥♥♥♥ should be measured in volume. Think about it. If someone has a 20cm ♥♥♥♥ but only like 3cm in diameter its not that much ♥♥♥♥. I get it would be harder to measure. You could probably use the formula of a truncted cone or cylinder.
If you fill a measuring jug full, put your ♥♥♥♥ in it so it overflows and measure how much water displaced you could find the volume of your ♥♥♥♥ that way. That’s how archimedes would do it

heeeeeeeeeeeeeeeeey.