Bandwidth & Download Time Calculator

Protocol overhead is the extra data added by networking protocols on top of your payload. TCP/IP headers, HTTP headers, TLS handshake, and acknowledgement packets typically add 5–10% overhead. This means a 100 Mbps connection delivers roughly 90–95 Mbps of actual data. For large file transfers, overhead is relatively small. For many small HTTP requests, overhead can dominate and effective throughput drops significantly.

ISPs advertise bandwidth in Mbps (megabits per second) while file sizes are shown in MB (megabytes), creating an 8x difference. A 100 Mbps connection downloads at 12.5 MB/s theoretically. Real-world speeds are lower due to: network congestion, Wi-Fi interference, server limitations, distance to CDN edge servers, and protocol overhead. Speeds also vary by time of day as ISPs share infrastructure among subscribers.

Theoretical peak speeds: 4G LTE up to 150 Mbps (typically 10–50 Mbps real-world), 5G Sub-6GHz up to 1 Gbps (typically 100–400 Mbps), 5G mmWave up to 10 Gbps (typically 1–3 Gbps in optimal conditions). Downloading a 1 GB file takes roughly 80–160 seconds on 4G vs 10–20 seconds on 5G Sub-6GHz. mmWave 5G can theoretically download 1 GB in under 1 second but requires being very close to a base station.

Bandwidth is the maximum data transfer rate (pipe width). Latency is the delay before transfer begins (pipe length). For large file downloads, bandwidth dominates: a 1 GB file on a 100 Mbps / 100ms latency connection takes about the same time as on 100 Mbps / 10ms — the extra 90ms startup is negligible. For many small requests, latency dominates: 100 requests at 100ms latency each consume 10 seconds of latency alone regardless of bandwidth.