Ethernet Goodput Calculator (Real Throughput and Frames per Second)
The real data rate you can expect on an Ethernet link once preamble, headers, checksum, inter-frame gap and IP/TCP headers are paid for, and how many frames per second the line carries.
Results
The dashed line marks the value you entered.
What this tool does
Every Ethernet frame costs 38 bytes on top of its payload: 8 bytes of preamble, 14 of header, 4 of checksum and a 12-byte idle gap. With a 1500-byte payload the frame efficiency is 97.5 %, and the IPv4 and TCP headers take another 40 bytes, leaving about 949 Mbit/s of application data on a gigabit link; the TCP timestamp option, 12 bytes more, brings it to the 941 Mbit/s a good file transfer usually shows. Small frames fare much worse: the smallest ones, 84 bytes on the wire, give the famous 1 488 095 frames per second on gigabit Ethernet, which is what a router or firewall is tested against.
Formula
wire bytes = 8 preamble + 14 header + payload (min 46) + 4 FCS + 12 gap = payload + 38 · goodput = rate × (MTU − IP/TCP headers) ÷ wire bytes · frames/s = rate ÷ (8 × wire bytes)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
lr | Link speed | Mbit/s |
mtu | Payload of each frame (the MTU) | B |
pr | Protocol carrying your data | — |
GP | Application data rate (goodput) | Mbit/s |
EF | Share of the line used by frame payload | % |
WB | Bytes each frame takes on the wire | B |
PP | Frames per second at full speed | fps |
FT | Time one frame occupies the line | µs |
PM | Frames per second with the smallest frames | fps |
Worked example
- Link speed1000 Mbit/s
- Payload of each frame (the MTU)1500 B
- Protocol carrying your data1
- Application data rate (goodput)949.3 Mbit/s
- Share of the line used by frame payload97.53 %
- Bytes each frame takes on the wire1538 B
- Frames per second at full speed81,274 fps
- Time one frame occupies the line12.30 µs
- Frames per second with the smallest frames1,488,095 fps
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.