How Much Fiber Do I Need for a 5G Cell Site? A Calculator and a Method You Can Defend

How much fiber does your rollout need? Run the numbers

Enter the numbers you know and the page returns fiber-km, cable-km, reels and a buy-by date. Start with site count, sectors, radios and the fronthaul design, then set the aggregation design. Open the advanced assumptions to change route lengths, reel lengths and buffers. Every default is an illustrative placeholder.

Where does the fiber go at a 5G cell site?

A site needs fibers in three places: up the tower to the radios, out along a lateral to an aggregation point, and, shared between about ten sites, along a trunk to the core. The lateral and the trunk hold 99% of the fiber-km, and the tower run holds about 1%. At the defaults, three sectors with two radios each need 12 fronthaul fibers under a dedicated design, plus 2 for backhaul. With 10% spares the lateral needs 16, so each site gets a 24-fiber cable, and each of the 5 trunks needs 53 fibers, a 72-fiber cable.

Figure 1 shows why the layers behave differently. The tower run is the shortest and is bought as one assembly per site. The lateral is multiplied by every site and runs a few kilometres. The trunk is multiplied by only 5 aggregation points but runs the longest, so it is the biggest layer by fiber-km even though it is the smallest by count. Trunks often close into a ring; see how many fibers a metro ring needs.

Figure 2 compares dedicated and shared fronthaul. Corning’s article explains that under CPRI each sector and band gets a dedicated fiber pair, so operators could drop 24 or 36 fibers at a cell site, and that with WDM the same tower can be served by 2 fibers. It was first published in 2018 and does not cover eCPRI. Ericsson’s January 2026 white paper adds that CPRI is constant-bitrate while eCPRI is packet-based, and gives an example in which a 100 MHz, 64-antenna carrier needs 300 Gbps over CPRI but 25 Gbps over optimized eCPRI. It gives no fiber counts, so the saving here is this model’s, not Ericsson’s: 22.5% fewer fiber-km, with unchanged cable-km. Poles that carry small cells may also carry city endpoints, covered in GPON for smart city.

Fiber types matter at each layer. Standard single-mode fiber is covered by ITU-T G.652, and bend-insensitive fiber by ITU-T G.657, the usual choice for tower and cabinet runs where cable turns tight corners. If you plan WDM, the channel plan comes from the ITU-T G.694.1 frequency grid. Check that every quote names the recommendation and category you designed for, because a substitute made under shortage pressure should be a design decision, not a purchasing one.

How much extra should you order beyond the fibers you light?

Order for the lit fibers plus five adjustments, and expect standard cable sizes to be the largest of them. In this example the adjustments take 5,016 lit fiber-km to a 9,508 fiber-km order, and rounding up to standard sizes alone adds 2,370.

Site access problems are the part of contingency teams rarely price, because each failed visit means a second crew trip. The Technician Checklist Generator turns your site acceptance steps into a checklist crews actually follow, which is the cheapest way to cut re-visits.

Figure 3 builds the order one step at a time. The fibers actually lit come to 5,016 fiber-km; the order is 9,508. A site needs 14 fibers and a tower needs 12, but cables come in 12 or 24, so the rounding step adds 2,370 fiber-km against 606 for the 10% spare allowance. Sizing is the decision to review first.

Figure 4 moves one input at a time. Site count and lateral length dominate: a 20% error in lateral length changes the order by 15.0%, while a 20% error in slack changes it by 1.8%. Cable sizes make some bars lopsided. Two sectors instead of three cut the order by 23%, because the lateral drops to a 12-fiber cable, but four sectors change nothing, because 18 to 20 fibers still fit 24. The trunk is the cliff: 48 fibers plus 10% spares is 53, which forces a 72-fiber cable, and trimming the design to 43 fibers would fit a 48-fiber cable.

Design moves the answer more than any buffer: a dedicated 6-sector, 3-radio site needs a 48-fiber lateral and the order rises to 13,876 fiber-km, about 1.5 times the default, while shared fronthaul brings it down to 7,366. That is why a page that quotes “fibers per site” without naming the fronthaul design is not safe to copy into a tender. Note that adding a third radio per sector changes nothing at these defaults, because 18 fronthaul fibers plus 2 backhaul still fit 24.

When do you need to buy the fiber?

Work backwards from the first build: buy-by date equals start date minus supplier lead time minus a shipping and QA buffer, and treat the lead time as a number to confirm, not assume. The reports below describe US builds and some are anonymous, so use them to set expectations and then get written quotes from your own suppliers.

In March 2026, Light Reading reported that some ISP leaders had received revised purchase orders with fiber cost increases of 70 to 80%, and that one BEAD-winning provider was told a loose tube cable it normally buys had a 52-week lead time. Corning denied that it was behind the increases. In July, Light Reading reported that Conexon told the FCC delivery times for non-BABA cable had risen by more than 40%. CRU Group’s OFC 2026 review says BABA-compliant fibre is largely sold out for 2026 with lead times over 50 weeks, and that some manufacturers have deprioritised BEAD orders in favor of hyperscale demand. Blandin on Broadband cited an anonymous source for normal lead times of 8 to 12 weeks.

Figure 5 applies those lead times to an example plan. If you order on 21 October 2026 with a 26-week lead time and a four-week buffer, the earliest start is 19 May 2027, ahead of a 1 July 2027 first build. The buy-by date for that case is 3 Dec 2026, 43 days from today. At 52 weeks the earliest start is 17 Nov 2027, about 20 weeks late. The 26-week figure is an assumed midpoint, not a reported one.

Figure 6 shows one way to cut exposure: one call-off per build wave. In this example, waves of 20, 20 and 10 sites cut the peak quantity on site from 9,508 to 3,803 fiber-km. The catch is commitment: phasing only protects you if the supplier agrees in writing to hold allocation for every call-off, and a supplier with a full order book may ask for project proof first.

How do you explain the number to finance, operations or a site partner?

Write the consequence, not the parameter. Every figure on this page becomes a sentence someone else has to accept: finance approving a purchase order, operations asked to change a fronthaul design, a landlord told when work starts. Engineers tend to write these as parameters. Readers need to know what changes for them and what you have secured. When a backhaul cut takes a site down, the Outage Communication Audit scores how clear your updates are. The examples below use this page’s illustrative numbers.

What should you check before placing the order?

Confirm eight things, and write down who owns each.

• Site count and build waves match the approved rollout plan, not the coverage target.
• The fronthaul design is fixed, dedicated or shared, and the radios per sector are confirmed with the equipment vendor.
• Lateral and trunk lengths are measured along the duct route, not drawn as straight lines.
• Every cable has a standard size, and the unused fibers are recorded as spare, not forgotten.
• Each layer has a named fiber type and ITU-T category, and every quote matches it.
• Lead time is in writing for each cable type and states whether the date is shipment or delivery.
• Call-offs are planned by build wave, and the supplier has committed allocation for each one.
• Site acceptance steps are agreed before the first delivery. The Technician Checklist Generator can turn them into a checklist crews use.

Frequently asked questions