GPON Power Budget Calculator

Verify your OLT-to-ONT optical budget in seconds, with splitter and fiber loss reference.

By FyberPay Engineering: operators running Kenyan ISP infrastructure.

Reviewed

GPON link from OLT to ONTOptical signal travels from the OLT, through feeder fiber, splitters, distribution fiber, drop fiber, and arrives at the ONT. Each segment subtracts dB from the link budget.OLT5 dBmFeeder10 km1×47 dBDist.2 km1×810.5 dBDrop0.5 kmONT-28 dBmTotal loss 24.48 dB · Budget 5.52 dB
Link is feasible
5.52 dB
budget remaining after margin
Total loss
24.48 dB
Fibers
4.38 dB
Splitters
17.50 dB
Splices
0.60 dB
Connectors
2.00 dB

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How to use this

  1. Enter your OLT and ONT optics. Pick TX power and RX sensitivity from your SFP datasheet: defaults match Class B+.
  2. Add your fiber lengths and splitters. Feeder, distribution, drop fibers plus stage 1 and stage 2 splitters cover almost every Kenyan ISP topology.
  3. Read the remaining budget. Green means the link closes with margin to spare. Red means you need a different splitter ratio, shorter fiber, or C+ optics.

How it works

The GPON link budget is the optical power available to be lost between OLT and ONT while still maintaining the ONT's minimum receive sensitivity. Per ITU-T G.984.21, Class B+ specifies an OLT TX of +1.5 to +5 dBm and an ONT RX sensitivity of -28 dBm, giving a nominal 28 dB budget at the high end.

Loss accumulates from three primary sources. Fibers contribute roughly 0.35 dB/km at 1490 nm downstream. Splitters dominate: 1:4 ≈ 7 dB, 1:8 ≈ 10.5 dB, 1:16 ≈ 13.5 dB, 1:32 ≈ 17 dB. Splices (0.1 dB each) and connectors (0.5 dB each) round out the math.

We subtract a fixed 3 dB safety margin from the result. This accounts for connector degradation, splice creep, and temperature drift over the plant's lifetime2.

In a Kenyan ISP context

In Kenya, most Tier-2 ISPs deploy 1:8 or 1:16 split ratios at the cabinet with a 1:4 at the OLT, keeping cabinet-to-home drops under 1 km. Class B+ SFPs are widely available from regional distributors and work for typical Nairobi or coastal town topologies. For longer rural runs (Naivasha, Eldoret, Kisumu hinterland), Class C+ extends the budget to ~32 dB and lets you reach beyond 20 km of feeder fiber3.

FAQ

What is a typical GPON power budget?
For Class B+ optics, the budget is around 28 dB (OLT TX +5 dBm minus ONT RX sensitivity -28 dBm minus a 3 dB margin). Class C+ extends this to about 32 dB.
Why does Stage 2 splitter loss matter most?
Splitters dominate the budget. A 1:32 splitter introduces roughly 17 dB of loss, more than 40 km of feeder fiber. Choose your splitter ratio before you choose fiber length.
How much margin should I keep?
We default to 3 dB. ITU G.984 recommends a fixed safety margin to account for splice degradation, connector wear, and temperature drift over the lifetime of the plant.
How we calculate this

budgetRemaining = (oltTx - ontRx) - totalLoss - safetyMargin

totalLoss = (feeder + dist + drop) × fiberLossPerKm + stage1 + stage2 + splices × 0.1 + connectors × 0.5

Defaults: 0.35 dB/km fiber (1490 nm), 3 dB safety margin, splitter losses per ITU typical figures.

Sources

  1. ITU-T G.984.2: Gigabit-capable Passive Optical Networks: Physical media dependent (PMD) layer specification · International Telecommunication Union · retrieved 2026-05-17
  2. Huawei MA5800-series GPON SFP optical specifications · Huawei · retrieved 2026-05-17
  3. GPON Power Budget Guidelines, Class B+ / C+ · FS.com Technical Documentation · retrieved 2026-05-17