Interframe Gap Calculator
Convert the 96-bit Ethernet interframe gap into nanoseconds at any line rate and see the bandwidth it costs.
Inputs
Interframe Gap
96.000ns
One Bit Time
1.0000ns
Preamble + SFD Time
64.000ns
Non-Frame Bytes per Frame
20bytes
Idle Time per Second
7.802ms
Bandwidth Lost to Gap + Preamble
1.300%
Step by step
Values used
Line rate = 1 Gbps; Average frame size = 1,518 bytes; Frame rate = 81,274 frames/s
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.
Bandwidth cost of the gap
overhead = 20 ÷ (frame bytes + 20).
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
How it works
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).
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.