Ethernet Throughput Calculator
Turn a line rate into real frame rate, Layer 2 throughput and TCP goodput after preamble, IFG, headers and FCS.
Inputs
Application Goodput
949.28Mbps
Frames per Second
81,274fps
Bytes on the Wire per Frame
1,538bytes
Layer 2 Throughput
987.00Mbps
Wire Efficiency
97.53%
Step by step
Values used
Line rate = 1,000 Mbps; IP packet size = 1,500 bytes; 802.1Q tagged = No; IP + TCP header inside the payload = 40 bytes
Ethernet Throughput
Each frame occupies payload + 14-byte header + 4-byte FCS + 4-byte optional tag on the wire, plus a fixed 20 bytes of 7-byte preamble, 1-byte SFD and 12-byte interframe gap.
Application goodput
goodput = frames/s × (payload − IP/TCP headers) × 8.
Application Goodput
= 949.28 Mbps
Frames per Second
= 81,274 fps
Bytes on the Wire per Frame
= 1,538 bytes
Layer 2 Throughput
= 987.00 Mbps
Wire Efficiency
= 97.53
How it works
Line rate is consumed by every byte time on the wire, not just the frame, so the 20 bytes of preamble and interframe gap are charged before anything else. Dividing line rate by the on-wire frame length gives the frame rate, and multiplying that by the useful payload gives the throughput a user actually sees. A gigabit link never delivers a gigabit: at 1500-byte packets it tops out near 949 Mbps of TCP goodput, and quoting the wrong figure in a capacity plan or an SLA is a habit that leads to surprise congestion.
Formulas
Ethernet Throughput
Each frame occupies payload + 14-byte header + 4-byte FCS + 4-byte optional tag on the wire, plus a fixed 20 bytes of 7-byte preamble, 1-byte SFD and 12-byte interframe gap.
- on wire
- Total byte times consumed per frame including preamble, SFD and IFG
- frames/s
- line rate ÷ (on-wire bytes × 8)
- goodput
- Bytes left for the application after IP and TCP headers
Application goodput
goodput = frames/s × (payload − IP/TCP headers) × 8.
Frequently Asked Questions
How is Ethernet Throughput calculated?
Each frame occupies payload + 14-byte header + 4-byte FCS + 4-byte optional tag on the wire, plus a fixed 20 bytes of 7-byte preamble, 1-byte SFD and 12-byte interframe gap. Line rate is consumed by every byte time on the wire, not just the frame, so the 20 bytes of preamble and interframe gap are charged before anything else. Dividing line rate by the on-wire frame length gives the frame rate, and multiplying that by the useful payload gives the throughput a user actually sees.
Why does Ethernet Throughput matter?
A gigabit link never delivers a gigabit: at 1500-byte packets it tops out near 949 Mbps of TCP goodput, and quoting the wrong figure in a capacity plan or an SLA is a habit that leads to surprise congestion.
What values do I need to enter?
This calculator takes 4 inputs: Line rate, IP packet size, 802.1Q tagged, IP + TCP header inside the payload. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why is small-packet throughput so much worse?
The 38–42 bytes of per-frame overhead are fixed. At a 64-byte frame you spend 84 byte times to carry 46 bytes of payload, so efficiency falls to about 55 percent — which is why packets-per-second, not bits-per-second, is the limit on firewalls and routers.