Tools · PON
PON power budget calculator: splitters and unbalanced taps
Pick the class, describe the cascades and the calculator works out the loss to every group of ONTs, the power each end receives and the margin against the class budget. The defaults are typical figures with their sources below. Type your own over any of them.
System class
The class power budget: the loss range its optics are built for. The loss from the OLT to every ONT has to fall between these two figures.
OLT
ONT
The class fills these in. If your OLT or ONT datasheet says otherwise, type its figures.
Cascades
grey means defaultA splitter divides power equally. An unbalanced tap sends a share to its drop and passes the rest down the line. Each drop feeds one ONT or its own splitter. Picking the ratios changes only the taps.
Fiber and joints along the route
Margin
The total is the customary design margin; how it splits into the three parts is our starting point, not a rule. Type your own figures.
Connectors and splices outside the splitters: the patch panel at the OLT, cable joints, the outlet at the ONT. The splitters' own joints are counted at every node by the connection method above.
Worst subscriber
Best subscriber
Speed per subscriber
| Down | Up |
|---|
The guaranteed rate is set by bandwidth allocation on the OLT and by the plan, not by the number of ONTs. Every doubling of ONTs on a port adds about 3 dB of loss and halves the bandwidth each one gets when all are busy.
The .xlsx file is for signed-in users: sign in with your email, no password. The link works for everyone.
Line diagram
Drawn from the cascades above. The feeder runs left to right, unbalanced taps drop down to their splitters. Each group of ONTs shows its upstream loss, colored against the class budget.
Every group of ONTs
Upstream at the ONT wavelength, downstream at the OLT wavelength. Received power uses the class minimum transmitter power. The .xlsx file carries this table, every input marked as default or your own, the cascades, the speeds and how it was calculated.
What else fits this line
Splitters, taps and classes
The figures the calculator starts from. The split is physics, 10·log10 of the power share. A real splitter loses more, and the typical loss is what designers put into the budget.
| Splitter | Split, dB | Typical, dB |
|---|---|---|
| 1×2 | 3.01 | 3.9 |
| 1×4 | 6.02 | 7.4 |
| 1×8 | 9.03 | 10.6 |
| 1×16 | 12.04 | 14.1 |
| 1×32 | 15.05 | 17.5 |
| 1×64 | 18.06 | 20.9 |
| 1×128 | 21.07 | 24.2 |
| Unbalanced tap | Through, dB | Drop, dB |
|---|---|---|
| 99/1 | 0.30 | 22.50 |
| 98/2* | 0.30 | 19.00 |
| 97/3* | 0.30 | 15.20 |
| 95/5 | 0.45 | 15.20 |
| 93/7* | 0.40 | 11.50 |
| 90/10 | 0.60 | 11.30 |
| 85/15 | 0.90 | 10.00 |
| 80/20 | 1.30 | 7.90 |
| 75/25 | 1.60 | 6.90 |
| 70/30 | 1.90 | 6.00 |
| 65/35 | 2.40 | 5.30 |
| 60/40 | 2.70 | 4.70 |
| 55/45 | 3.10 | 4.10 |
| 50/50 | 3.60 | 3.60 |
| Class | Line loss, dB | Down / up, nm | OLT transmitter / ONT sensitivity, dBm | Source |
|---|---|---|---|---|
| GPON A | 5–20 | 1490 / 1310 | 0.0…4.0 / −21 | ITU-T G.984.2 |
| GPON B | 10–25 | 1490 / 1310 | 5.0…9.0 / −21 | ITU-T G.984.2 |
| GPON B+ | 13–28 | 1490 / 1310 | 1.5…5.0 / −27 | ITU-T G.984.2 |
| GPON C | 15–30 | 1490 / 1310 | 3.0…7.0 / −28 | ITU-T G.984.2 |
| GPON C+ | 17–32 | 1490 / 1310 | 3.0…7.0 / −30 | ITU-T G.984.2 |
| GPON C++ | 17–32 | 1490 / 1310 | 4.5…10.0 / −30 | FS.com, PPC, 6COMGIGA |
| XG-PON N1 | 14–29 | 1577 / 1270 | 2.0…6.0 / −28 | ITU-T G.987.2 |
| XG-PON N2 | 16–31 | 1577 / 1270 | 4.0…8.0 / −28 | ITU-T G.987.2 |
| XG-PON N2b | 16–31 | 1577 / 1270 | 10.5…12.5 / −22 | ITU-T G.987.2 |
| XG-PON E1 | 18–33 | 1577 / 1270 | 6.0…10.0 / −28 | ITU-T G.987.2 |
| XG-PON E2 | 20–35 | 1577 / 1270 | 8.0…12.0 / −28 | ITU-T G.987.2 |
| XG-PON E2b | 20–35 | 1577 / 1270 | 14.5…16.5 / −22 | ITU-T G.987.2 |
| XGS-PON N1 | 14–29 | 1577 / 1270 | 2.0…5.0 / −28 | ITU-T G.9807.1 |
| XGS-PON N2 | 16–31 | 1577 / 1270 | 4.0…7.0 / −28 | ITU-T G.9807.1 |
| XGS-PON E1 | 18–33 | 1577 / 1270 | 6.0…9.0 / −28 | ITU-T G.9807.1 |
| XGS-PON E2 | 20–35 | 1577 / 1270 | 8.0…11.0 / −28 | ITU-T G.9807.1 |
| NG-PON2 N1 | 14–29 | 1600 / 1535 | 3.0…7.0 / −28 | ITU-T G.989.2 |
| NG-PON2 N2 | 16–31 | 1600 / 1535 | 5.0…9.0 / −28 | ITU-T G.989.2 |
| NG-PON2 E1 | 18–33 | 1600 / 1535 | 7.0…11.0 / −28 | ITU-T G.989.2 |
| NG-PON2 E2 | 20–35 | 1600 / 1535 | 9.0…11.0 / −28 | ITU-T G.989.2 |
Classes: ITU-T G.984.2 (08/2019) for GPON and G.9807.1 (02/2023) for XGS-PON. GPON C++ is not an ITU class: its figures are the most cautious ones in the module datasheets of FS.com, PPC and 6COMGIGA, and its line loss range is taken as in C+. Splitters: the maximum loss from ITU-T G.671 (11/2025), the figure designers put into a budget; 1:128 from manufacturer datasheets. Taps: two-window maximums from manufacturer tables; the ratios marked * rest on a single source, so check the datasheet. Connector 0.5 dB and splice 0.1 dB per ITU-T G.671. Fiber attenuation from cable datasheets; at 1270 and 1577 nm it is our estimate. Margin 3 dB, as in design practice.
GPON A, B and C: ITU-T G.984.2. XG-PON: ITU-T G.987.2; N2 and E2 are the N2a and E2a of the Recommendation, while N2b and E2b pair a stronger OLT with a less sensitive ONT. NG-PON2: ITU-T G.989.2, a link without an amplifier at the OLT (Type A). Its power is counted after the wavelength multiplexer, so add the multiplexer loss under Other. Fiber attenuation at the NG-PON2 wavelengths is taken from the nearest wavelengths we have a figure for, and the payload share of XG-PON and NG-PON2 is taken as for XGS-PON.
How the calculator works
The loss to a group of ONTs is the sum of everything on its path: the fiber, the splitters and taps the signal passes through, their joints, the connectors and splices on the route, and the margin. Upstream is calculated at the ONT wavelength and downstream at the OLT wavelength, because fiber loses more at the shorter one.
A balanced splitter divides the power equally: every doubling of outputs costs 3 dB on paper and a little more in a real device. An unbalanced tap divides it unevenly, and its two legs lose different amounts: on a 90/10 tap the feeder keeps most of the light and the drop gets a tenth.
The class sets the loss range its optics work within. Above the upper bound the farthest ONT cannot reach the OLT. Below the lower bound the nearest ONT gets so much light that its receiver overloads. The calculator checks both ends of the network, not just the worst one.
The connection method matters more than it looks. Each splitter or tap the signal passes adds its input and output joints, and on a bus the feeder goes through every node. Connectors there cost more than splices at each step.
A bus of unbalanced taps
A bus runs one feeder fiber along a street or a village. At each node an unbalanced tap sends a share of the power to a small splitter for the nearby houses and passes the rest on. It is built where a tree would need long cables to every cabinet.
The ratios change along the line: the first node takes little, the last ones take more, so that every node gets about the same power. Pick the tap ratios does this for you: it tries every ratio at every node, starting from the end of the line, and keeps the set where the worst subscriber loses least.
On an OTDR trace an unbalanced tap does not look like a balanced splitter: a small step on the through leg and a deep one on the drop. An OTDR that does not know the tap ratios may report it as a bad connector or a bend, and the acceptance test fails. Compare the step on the trace with the through and drop figures of that tap in the table above.
Where the calculation can differ from the field
Typical figures describe the average device. A particular splitter, connector or splice can lose more or less, and its datasheet or a measurement settles it. Type the figure from the datasheet over the default, and the file you download will mark it as your own.
The margin covers what the drawing does not show: ageing, repairs, a splice redone after a cable cut. The class budget is the limit of the optics, not a target to fill.
Speed per subscriber is shared bandwidth divided by the number of ONTs, which is the floor when all of them download at once. In practice few download at the same moment, and the plan and the OLT bandwidth allocation decide what each gets.
Questions
How much does a 1:8 splitter lose?
The split itself is 9.03 dB: the power is divided into eight. A real 1:8 splitter loses more, and the typical figure is in the table above. The datasheet of your splitter gives the exact value; type it into the cascade.
What is the splitter loss formula?
10·log10 N for a balanced 1:N splitter, so each doubling of outputs adds about 3 dB. For an unbalanced tap each leg loses 10·log10 of its share: on a 70/30 tap the 30 % leg loses about 5.2 dB and the 70 % leg about 1.5 dB, before the device's own loss.
Can I connect one splitter after another?
Yes, that is a cascade: a 1:4 followed by 1:8 gives 32 outputs, like one 1:32 splitter. The loss adds up in dB, and the extra joints between the stages add a little more. Describe the cascades above and the calculator adds everything up.
How many subscribers can one PON port serve?
As many as the budget allows and the bandwidth is enough for. The budget limits the split and the distance; the bandwidth is shared, so more ONTs means less for each when all are busy. The speed block shows both for your layout.