SFP & QSFP Compatibility Checker and Optical Link Budget Calculator

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Engineering inputs

Set the engineering assumptions and design parameters.

Transceiver and fiber inputs

Both ends must use the same link rate, media and compatible optical interface unless the hosts provide an explicit gearbox, breakout or rate-adaptation mode. This V1 model expects the same nominal wavelength and does not validate BiDi complementary wavelengths or individual WDM lanes.

Common link preset

Module A

Form factor

Aggregate rate (Gbps)

Lane count

Media

Wavelength (nm)

Connector

Minimum Tx (dBm)

Maximum Tx (dBm)

Rx sensitivity (dBm)

Rx overload (dBm)

Module B

Form factor

Aggregate rate (Gbps)

Lane count

Media

Wavelength (nm)

Connector

Minimum Tx (dBm)

Maximum Tx (dBm)

Rx sensitivity (dBm)

Rx overload (dBm)

Fiber link

Fiber type

Distance (km)

Attenuation (dB/km)

Connector count

Loss per connector (dB)

Splice count

Loss per splice (dB)

Engineering margin (dB)

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Engineering results

Review calculated capacity, limits and design checks.

Compatibility result

Estimated receive power—

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Physical link loss—

Sensitivity margin—

Design margin—

Overload headroom—

How to check SFP and QSFP module compatibility

1. Match Ethernet rate and lanes

SFP+ commonly carries one 10 Gbps lane, SFP28 one 25 Gbps lane, QSFP+ four 10 Gbps lanes and QSFP28 four 25 Gbps lanes. Matching cages alone does not guarantee link compatibility.

2. Match fiber and optical interface

Both modules must use a compatible optical interface and suitable fiber type. This tool’s nominal-wavelength check is for symmetric links; verify complementary Tx/Rx wavelengths for BiDi and every lane wavelength for CWDM, LR4 or other WDM optics from the two module datasheets.

3. Verify both directions

For A→B and B→A, minimum transmitter power is checked against receiver sensitivity after link loss and engineering margin. Maximum transmitter power is checked against receiver overload. Include every connector and splice.

SFP+ vs SFP28 and QSFP+ vs QSFP28 compatibility

An SFP28 cage may support an SFP+ module when the switch or NIC explicitly supports 10G operation, but the module at the opposite end must also run the same rate. Likewise, QSFP28 equipment may support QSFP+ or breakout modes only when the host platform documents that capability. This calculator checks the passive-link requirements; always confirm vendor coding, host firmware, FEC, breakout mapping and Ethernet standard in the equipment datasheet.

Optical transceiver link budget formula

Minimum receive power = minimum Tx − physical link loss; maximum receive power = maximum Tx − physical link loss. Each direction must remain above sensitivity after engineering margin and at or below overload. The summary shows the worst directional margin. PASS is a planning estimate, not a guarantee of host-vendor interoperability.

Can I connect 10G SFP+ to 25G SFP28?

Not at different line rates. It can work only if both hosts and both modules operate at the same supported rate, commonly 10G in an SFP28 cage with explicit backward compatibility.

Can single-mode and multimode optical modules communicate?

No. The optics, fiber type and wavelength plan must form a supported link. Mixing SMF and MMF modules is not a valid production design.

Why is receiver overload checked?

A very short link with maximum transmitter power can exceed the receiver maximum input. This tool checks both directions with maximum Tx; an attenuator may be required when overload headroom is negative.

Does PASS guarantee a branded switch accepts the module?

No. Vendor coding and host firmware policies are outside the optical budget. Confirm the module part number in the switch or NIC compatibility list.

Can I install a QSFP28 module in a QSFP-DD port?

Only when the host vendor documents backward compatibility and the port is configured for the module rate and lane mode. A mechanically compatible cage does not prove firmware, FEC, breakout or optical-interface support.

SFP and QSFP engineering references

This tool does not query a vendor compatibility database or validate module EEPROM coding, host firmware, FEC, breakout maps, temperature class, power class, BiDi pairing or WDM lane plans. Confirm exact part numbers at both hosts. Last reviewed: 2026-08-31.

SFP & QSFP Compatibility Checker