Fiber Link Budget Calculator

Visualization unavailable

Planning profile:

Start from a common route shape or keep custom values.

Minimum transmit power:

Conservative transmitter output from the optic datasheet.

dBm

Receiver sensitivity:

Lowest acceptable receive level from the optic datasheet.

dBm

Route distance:

Changing the unit converts the displayed value without changing the physical route.

Value

Fiber attenuation:

Changing the basis converts the rate without changing attenuation per physical distance.

Value Basis

Mated connections:

Enter the count and design or measured insertion loss for each connection.

Count Loss each dB

Splices:

Enter the count and insertion loss for each splice.

Count Loss each dB

Passive component loss:

Total additional passive loss for this path.

{{ formatNumber(Number(passive_loss_db), 2) }} dB

Value dB

Required reserve:

Minimum operating margin to preserve after modeled loss.

{{ formatNumber(Number(required_reserve_db), 1) }} dB

Value dB

Receiver overload check:

Disabled by default, so it does not change the normal link result.

Maximum receive power:

Estimated receive power above this limit needs attenuation.

dBm

Equipment/dispersion:

Optional additive loss allowance.

Measurement uncertainty:

Optional additive loss for field-test uncertainty.

Reach chart horizon:

Set the furthest distance shown in the reach curve.

Display precision:

Choose compact or detailed display values.

Budget item	Value	Basis	Copy
{{ row.label }}	{{ row.value }}	{{ row.basis }}

An optical receiver needs light to arrive inside a usable power window. Too little power falls below sensitivity and can produce errors or loss of link; too much can overload the receiver. Every fiber span, mated connection, splice, splitter, wavelength-dependent attenuation, and engineering allowance moves the received level.

A link budget compares the weakest guaranteed transmitter output with the receiver's minimum acceptable input. Those endpoint values are in dBm, an absolute power level. Cable and component losses are in dB, a relative change that can be added along the route. Subtracting all route losses from transmitter power estimates the receive level; comparing that level with sensitivity gives operating margin.

Fiber link budget quantities
Quantity	Meaning	Typical evidence
Transmit power	Lowest optical output used for a conservative plan	Optic datasheet
Receiver sensitivity	Lowest receive power that meets the specified performance	Optic datasheet
Path loss	Fiber, connectors, splices, passives, penalties, and measurement allowance	Design values and field measurements
Required reserve	Margin deliberately kept for aging, contamination, repairs, and uncertainty	Engineering policy

A positive margin is not the same as a robust design. A route can remain above sensitivity yet miss its required reserve, and a very short route can have ample low-power margin while exceeding the receiver's maximum input. Budget estimates should therefore use the correct wavelength, optic pair, route length, component count, and worst-case specifications, then be checked against the installed path.

How to Use This Tool:

Build the route from conservative endpoint values, then account for every planned loss once.

Choose a Planning profile as a starting shape or keep custom values. Replace example values with the exact wavelength and optic specifications for the link.
Enter Minimum transmit power and Receiver sensitivity from the datasheets, then set physical route distance and fiber attenuation on matching km or mile bases.
Count mated connector pairs and splices, enter loss per item, and add splitter, coupler, or other Passive component loss.
Set the required reserve. Add equipment penalties or measurement uncertainty under Advanced only when they are documented and are not already included elsewhere.
Enable Receiver overload check when the maximum receive-power specification is known, then read the final status together with estimated receive power and reserve delta.

Interpreting Results:

Reserve met means operating margin is at least the required reserve.
Reserve narrow means the reserve is met by less than 1 dB. Small field differences could consume it.
Reserve shortfall means estimated receive power remains at or above sensitivity, but the specified reserve is not met.
Below sensitivity means total modeled loss exceeds the available power budget.
Receiver overload means the overload check is enabled and estimated receive power is greater than the entered maximum.

Technical Details:

Optical losses combine additively in dB. Fiber loss scales with distance, while connectors, splices, passive components, penalties, and uncertainty are fixed route terms for a given design.

Formula Core:

The complete power and margin chain is:

\begin{array}{rcl} B & = & P_{t} - P_{s} \\ L_{f} & = & d α \\ L & = & L_{f} + n_{c} l_{c} + n_{s} l_{s} + L_{p} + L_{a} \\ P_{r} & = & P_{t} - L \\ M & = & B - L \\ Δ M_{r} & = & M - M_{r} \end{array}

P_t is minimum transmit power in dBm, P_s is receiver sensitivity in dBm, B is power budget in dB, d is distance, and α is fiber attenuation per distance unit. Connector and splice counts are n_c and n_s; their individual losses are l_c and l_s. L_p is passive loss, L_a combines penalties and uncertainty, P_r is estimated receive power, M is operating margin, and M_r is required reserve.

Reach and Overload Rules:

Maximum distance spends the remaining budget on fiber after fixed losses and reserve:

d_{\max} = \max (0, \frac{B - M_{r} - L_{fixed}}{α})

Sensitivity is met when operating margin is greater than or equal to 0 dB. Reserve is met when reserve delta is greater than or equal to 0 dB. Overload is flagged only when the check is enabled and estimated receive power is strictly greater than the entered receiver maximum; equality is accepted.

Accuracy Notes:

The result is a deterministic planning estimate, not an optical time-domain reflectometer trace or acceptance test. Connector condition, launch quality, bends, wavelength, temperature, repair history, splitter variation, and instrument uncertainty can move the installed result.

Do not add the same guard band twice. If a vendor's stated penalty already includes a loss, keep that value out of the separate uncertainty entry. Use minimum transmitter output and minimum receiver sensitivity from compatible optics rather than typical readings.

Worked Example:

An 8 km, 1310 nm planning case uses −3 dBm minimum transmit power, −18 dBm sensitivity, 0.35 dB/km fiber, four 0.5 dB connections, six 0.1 dB splices, and a 3 dB reserve. Total loss is 5.4 dB, estimated receive power is −8.4 dBm, operating margin is 9.6 dB, and reserve delta is 6.6 dB. With those same fixed losses and attenuation, reserve-limited reach is about 26.86 km.

References:

PA-A6 Overview: Optical Power Budget and Power Margin, Cisco.
Calculating Fiber Optic Loss Budgets, The Fiber Optic Association.