Ethernet Overhead Calculator
Calculate the fixed Ethernet framing overhead (preamble, header, FCS, inter-frame gap) and its impact on effective throughput.
Inputs
Total Overhead per Frame
38bytes
Total Frame Size on Wire
1,498bytes
Link Efficiency
97.46%
Effective Throughput
974.63Mbps
Step by step
Values used
Payload Size = 1,460 bytes; Link Speed = 1,000 Mbps
Ethernet framing overhead
overhead = preamble(8) + header(14) + FCS(4) + IFG(12) = 38 bytes/frame
Total Overhead per Frame
= 38 bytes
Total Frame Size on Wire
= 1,498 bytes
Link Efficiency
= 97.46
Effective Throughput
= 974.63 Mbps
How it works
Every Ethernet frame carries fixed overhead beyond the payload: an 8-byte preamble for clock synchronization, a 14-byte header (destination MAC, source MAC, type/length), a 4-byte Frame Check Sequence for error detection, and a 12-byte Inter-Frame Gap that separates consecutive frames on the wire — totaling 38 bytes per frame. This overhead is constant regardless of payload size, so it represents a larger percentage loss for small frames than for large ones, directly reducing the effective throughput available for actual data below the link's rated speed.
Formula
Ethernet framing overhead
overhead = preamble(8) + header(14) + FCS(4) + IFG(12) = 38 bytes/frame
- h
- Total fixed overhead per Ethernet frame
Frequently Asked Questions
What are the four components of Ethernet frame overhead?
The 8-byte preamble (plus start frame delimiter) synchronizes the receiver's clock before the frame proper begins; the 14-byte header holds destination MAC, source MAC, and EtherType/length; the 4-byte Frame Check Sequence is a CRC used to detect transmission errors; and the 12-byte Inter-Frame Gap is idle time enforced between frames, totaling 38 bytes of non-payload data per frame.
Why does this overhead matter more on a link full of small packets?
The 38-byte overhead is fixed per frame regardless of payload size, so a 64-byte minimum-size frame loses over 37% of its wire time to overhead, while a 1500-byte frame loses only about 2.5%. Workloads dominated by small packets (VoIP, gaming, many small API calls) therefore see proportionally lower effective throughput than large, bulk transfers.
Is the Inter-Frame Gap actually part of the frame?
No — it's idle time (minimum 96 bit-times) enforced on the wire between the end of one frame and the start of the next, not data within the frame itself. It is still counted as overhead because it consumes link time that cannot carry payload, reducing achievable throughput exactly like the other components.