Ethernet Throughput Calculator
Turn a line rate into real frame rate, Layer 2 throughput and TCP goodput after preamble, IFG, headers and FCS.
About Ethernet Throughput Calculator
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.
Worked example
With the default values below, Ethernet Throughput Calculator returns Application Goodput of 949.28. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Line rateminimum 1 Mbps
- 1,000 Mbps
- IP packet sizeaccepts 20–9,000 bytes
- 1,500 bytes
- 802.1Q tagged
- No
- IP + TCP header inside the payloadaccepts 0–120 bytes
- 40 bytes
Results
- Frames per Second
- 81,274 fps
- Bytes on the Wire per Frame
- 1,538 bytes
- Layer 2 Throughput
- 987.00 Mbps
- Application Goodput
- 949.28 Mbps
- Wire Efficiency
- 97.53%
Step by step
- 1Values used
- 2Ethernet Throughput
- 3Application goodput
- 4Application Goodput= 949.28 Mbps
- 5Frames per Second= 81,274 fps
- 6Bytes on the Wire per Frame= 1,538 bytes
- 7Layer 2 Throughput= 987.00 Mbps
- 8Wire Efficiency= 97.53
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.