Don't really understand what it is you want to measure. You've got the BCD(bolt circle diameter) already, and you can just count the teeth.
The standard BMX hub spacing measurement for most modern BMX bikes is 110mm.
It will if you have bmx (or bmx style) cranks.
No. Some BMX chainrings have the same 4/5 bolt pattern as road bikes, but most use another method of attachment to the crank. If it is a 4/5 bolt chainring you first have to measure the bolt circle diameter to see how that fits. I'll post a link on that. Next is the thickness of the chain rings. BMXes are single-speed and use a thicker chain. Most road bikes have external gears and need a thinner, more flexible chain to work. I'm not sure if a road bike chain will fit on a BMX chainring. (Unless it's a single-speed road bike of course. Then you can run a BMX-style chain and all can be made to work.)
To measure BMX handlebars accurately, use a measuring tape to determine the width of the handlebars from end to end. Additionally, measure the rise of the handlebars from the center of the stem to the top of the bars. These measurements will help ensure a proper fit for your BMX bike.
You measure it. A ruler and a caliper are useful.
BMX bikes all have the same size (20") wheels, so they're very similar in size. Doesn't matter that much as they are mainly ridden standing up anyhow.
Different BMXes have different axle sizes. Easiest is to measure what you've got.
BMX
you spell it BMX
Chain alignment is off between the freewheel and front chainring. Also check chain tension when installing the back wheel.
Different BMXes have different axle sizes. Easiest is to measure what you've got.
It is where bmx rider race.