JavaScript (ES6), 78 74 bytes
f=(n,i)=>n<999.5?i?n.toPrecision(n<1^3)+' KMG'[i]+'iB':n+'B':f(n/1024,-~i)<input oninput=o.textContent=f(this.value)><pre id=o>Edit: Saved 4 bytes thanks to @Arnauld.
JavaScript (ES6),
Neil
- 177.3k
- 12
- 74
- 281