how to use mkdosfs command to do partition of 200MB with FAT32

Question

I want to do two partitions for my SD card with FAT and EXT4 using Ubuntu.

For this, I found two commands:

mkdosfs /dev/sda1 -n 
mke2fs /dev/sda1 -L

But how should I specify the size, for FAT I need 200MB and rest with EXT4.

When tried to give mkdosfs /dev/sda1 -n I got an error.

sudo mkdosfs /dev/sda
mkfs.fat 3.0.28 (2015-05-16)
mkdosfs: unable to open /dev/sda: Device or resource busy