Hi, I am making the number 70 out of chocolate, to go on top of a 2 tier cake- each tier is 4inches tall, and they are 8'' inch and 10'' inch tiers in diameter. How tall should the number 70 be?
Whatever you think looks right. To get a good idea of how it will look, arrange the cake tins you'll be using to resemble the cake and cut a rough '70' the size you think you'll want out of cardstock, holding it in position to see how it looks.
Are there any general rules? Should it be the same height or lower then the bottom tiers?
Personally, I think they should be shorter than the tiers. My cakes are 4" high too, but my numbers when I've done them have been around 2.5". This for one or two tiers. For a tall cake such as 4 or more tiers, the small numbers might look a little "lost", so I would probably make them bigger.