Interframe Gap Calculator
Convert the 96-bit Ethernet interframe gap into nanoseconds at any line rate and see the bandwidth it costs.
About Interframe Gap Calculator
The gap is specified in bit times, not seconds, so it shrinks as the link gets faster — 9.6 µs at 10 Mbps, 96 ns at 1 Gbps and 0.96 ns at 100 Gbps. Combined with the 64-bit preamble and SFD it burns 20 byte times before every frame, which is bandwidth you can never recover. The gap is why a 10 Gbps port cannot forward 14.88 million 64-byte frames plus anything else, and it is the term people forget when their measured throughput lands a few percent below the theoretical figure.
Formulas
Interframe Gap
The interframe gap is fixed at 96 bit times, so its duration is 96 ÷ line rate; one bit time at R Mbps is 1000/R nanoseconds.
- 96 bit times
- IEEE 802.3 minimum interframe gap
- bit time
- 1000 / line rate in Mbps, in nanoseconds
- 20 bytes
- 7-byte preamble + 1-byte SFD + 12-byte IFG
Bandwidth cost of the gap
overhead = 20 ÷ (frame bytes + 20).
Worked example
With the default values below, Interframe Gap Calculator returns Interframe Gap of 96.000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Line rateone of 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 25 Gbps, 40 Gbps, 100 Gbps, 400 Gbps
- 1 Gbps
- Average frame sizeaccepts 64–9,018 bytes
- 1,518 bytes
- Frame rateminimum 0 frames/s
- 81,274 frames/s
Results
- Interframe Gap
- 96.000 ns
- One Bit Time
- 1.0000 ns
- Preamble + SFD Time
- 64.000 ns
- Non-Frame Bytes per Frame
- 20 bytes
- Idle Time per Second
- 7.802 ms
- Bandwidth Lost to Gap + Preamble
- 1.300%
Step by step
- 1Values used
- 2Interframe Gap
- 3Bandwidth cost of the gap
- 4Interframe Gap= 96.000 ns
- 5One Bit Time= 1.0000 ns
- 6Preamble + SFD Time= 64.000 ns
- 7Non-Frame Bytes per Frame= 20 bytes
- 8Idle Time per Second= 7.802 ms
- 9Bandwidth Lost to Gap + Preamble= 1.300
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 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 Interframe Gap calculated?
The interframe gap is fixed at 96 bit times, so its duration is 96 ÷ line rate; one bit time at R Mbps is 1000/R nanoseconds. The gap is specified in bit times, not seconds, so it shrinks as the link gets faster — 9.6 µs at 10 Mbps, 96 ns at 1 Gbps and 0.96 ns at 100 Gbps. Combined with the 64-bit preamble and SFD it burns 20 byte times before every frame, which is bandwidth you can never recover.
Why does Interframe Gap matter?
The gap is why a 10 Gbps port cannot forward 14.88 million 64-byte frames plus anything else, and it is the term people forget when their measured throughput lands a few percent below the theoretical figure.
What values do I need to enter?
This calculator takes 3 inputs: Line rate, Average frame size, Frame rate. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.