Calculator Inputs
The calculator area uses three columns on large screens, two on medium screens, and one on mobile screens.
Formula Used
The calculator treats user payload as the useful data field and counts every non-payload byte as overhead.
VLAN bytes = VLAN tag count × bytes per VLAN tag
Frame bytes without padding = Ethernet header + FCS + VLAN bytes + additional encapsulation + payload
Padding bytes = max(0, minimum frame bytes − frame bytes without padding)
Frame bytes = frame bytes without padding + padding bytes
Wire bytes per frame = frame bytes + preamble/SFD + IFG
Overhead bytes per frame = wire bytes per frame − payload bytes
Payload efficiency (%) = payload bytes ÷ wire bytes per frame × 100
Goodput (Mbps) = line rate × payload efficiency
Transmission time (seconds) = total wire bits ÷ line rate in bits per second
Minimum frame enforcement is useful when small payloads require padding to reach the classic 64-byte Ethernet frame size, excluding preamble and IFG.
How to Use This Calculator
- Enter the payload size carried inside each Ethernet frame.
- Enter the number of frames you plan to send.
- Select the line rate in Mbps for goodput and timing results.
- Set header, FCS, VLAN, and extra encapsulation fields to match your environment.
- Choose whether preamble and IFG should count toward wire utilization.
- Keep minimum frame enforcement enabled for realistic small-packet calculations.
- Press the calculate button to show results below the header and above the form.
- Download the computed summary as CSV or PDF when needed.
Example Data Table
These sample rows assume a 1 Gbps link, preamble enabled, IFG enabled, no VLAN tags, and minimum frame enforcement turned on.
| Payload Bytes | Padding Bytes | Wire Bytes per Frame | Overhead Bytes per Frame | Efficiency | Goodput at 1 Gbps |
|---|---|---|---|---|---|
| 46 | 0 | 84 | 38 | 54.76% | 547.62 Mbps |
| 128 | 0 | 166 | 38 | 77.11% | 771.08 Mbps |
| 512 | 0 | 550 | 38 | 93.09% | 930.91 Mbps |
| 1,500 | 0 | 1,538 | 38 | 97.53% | 975.29 Mbps |
| 9,000 | 0 | 9,038 | 38 | 99.58% | 995.80 Mbps |
Frequently Asked Questions
1. What does Ethernet overhead mean?
Ethernet overhead is every transmitted byte that is not your application payload. It can include the Ethernet header, FCS, VLAN tags, padding, preamble, and interframe gap, depending on how you model the wire budget.
2. Why is IFG included here?
IFG does not sit inside the frame, but it still consumes time on the medium. Including it gives a more realistic picture of usable line rate and packet-per-second limits.
3. Why does a small payload sometimes show padding?
Classic Ethernet frames must meet a minimum size. When the payload and header fields are too small, padding is inserted so the frame reaches the minimum valid length.
4. What is the difference between efficiency and goodput?
Efficiency is the payload share of total on-wire bytes. Goodput converts that percentage into Mbps by applying it to the selected line rate.
5. Should I count VLAN tags as overhead?
Yes. VLAN tags add bytes to each frame and reduce payload efficiency. If your path uses QinQ or stacked tagging, increase the VLAN tag count accordingly.
6. Can I use this for jumbo frames?
Yes. Select the jumbo profile or enter a custom payload limit. The calculator will still compute values even if you exceed the selected profile, but it will warn you.
7. What should I place in additional encapsulation bytes?
Use that field for extra per-frame bytes not already modeled. Examples include service headers, security tags, or provider-specific encapsulation added between payload and physical transmission.
8. Do CSV and PDF contain the current result?
Yes. CSV downloads the active input and output set. PDF captures the visible result section, including the summary, detailed table, and chart area shown on the page.