Estimate time and data for game downloads.
Connection speed is quoted in megabits per second while downloads are sized in gigabytes, and that factor of eight is where most estimates go wrong. Converting gigabytes to megabits and dividing by throughput gives the time. Throughput is not the headline speed: protocol overhead, server limits and Wi-Fi losses typically leave eighty to ninety percent, which is why the efficiency factor is an explicit input.
Download time
Seconds = download size in GB x 8000 megabits / (line speed in Mbps x efficiency)
Data cap impact
Share of cap = download size / monthly data cap x 100
Common causes are a congested content delivery server, Wi-Fi rather than Ethernet, background traffic on the same line and evening peak-hour contention. Lower the efficiency figure to match what you observe.
Frequently. Many titles need the download plus room to unpack, so free space of roughly one and a half times the download is a safe assumption on console.