5G NR Throughput Calculation — Worked Example for 100 MHz @ 30 kHz

Engineers ask "what throughput will I get from a 100 MHz 5G cell?" all the time. The textbook answer is "depends." The real answer is a specific number, derivable in 5 minutes once you know the steps. Here's the worked example.

The Cell Configuration

Channel bandwidth: 100 MHz. Subcarrier spacing: 30 kHz (μ=1, FR1 default). MCS Table: 2 (256-QAM). Target MCS: 16 (Qm=8, code rate 0.5547). Layers: 4 (rank 4, typical mid-band 4×4 MIMO). Slot duration: 0.5 ms.

Step 1 · Number of PRBs

From TS 38.101-1 Table 5.3.2-1, 100 MHz @ 30 kHz SCS = 273 PRBs. Each PRB has 12 subcarriers, so total SCs = 273 × 12 = 3,276.

Step 2 · Number of REs Available for PDSCH per Slot

Per TS 38.214 §5.1.3.2:

• SCs per PRB: 12
• Symbols per slot: 14 (Normal CP)
• DMRS overhead: 12 REs (Type 1, 1 symbol, 1 port — typical config)
• Other overheads (PDCCH, CSI-RS, PT-RS): ~8% of REs
• N_RE per PRB = 12 × 14 - 12 - 8 = ~148 REs/PRB

Total N_RE per slot = 148 × 273 = 40,404 REs.

Step 3 · Bits per RE from MCS

MCS 16 in Table 2: Qm = 8 (256-QAM), code rate R = 0.5547. Bits per RE = Qm × R × layers = 8 × 0.5547 × 4 = 17.75 bits per RE per slot.

Step 4 · TBS Computation

Intermediate N'_info = N_RE × Qm × R × layers = 40,404 × 17.75 = 717,171 bits.

This is rounded to the nearest table entry per TS 38.214 §5.1.3.2 step 3 — typically falls onto a specific TBS like 720,008 bits. For this example we'll use ~720,000 bits per slot.

Step 5 · Per-Slot to Per-Second

Slot duration at μ=1 is 0.5 ms = 500 μs. Slots per second = 1,000,000 / 500 = 2,000 slots/sec.

Per-layer per-cell throughput = 720,000 bits/slot × 2,000 slots/sec = 1,440,000,000 bits/sec ≈ 1.44 Gbps.

Step 6 · Reality Check

Actual peak in published tests typically lands at 1.0-1.3 Gbps for this exact configuration. Why the gap?

• HARQ retransmissions consume slots (~10-20% of slots)
• BLER target 10% before HARQ further reduces
• UE-side processing delays mean not every slot delivers a fresh TB
• SS Burst Set + paging consume ~5% of slots
• UE may not always operate at MCS 16 — link adaptation drops on poor SINR

The Quick Mental Formula

For a back-of-envelope estimate:

Throughput ≈ N_PRB × 12 × 14 × Qm × R × layers / slot_duration

Plug 273, 8, 0.5547, 4, and 0.0005 — you get ~1.7 Gbps. Discount 20-30% for overheads and HARQ — ~1.2-1.3 Gbps real-world.

The 99-lesson course covers this calculation step-by-step in Lesson 2-1-6 (PDSCH Throughput Calculator) with an interactive web tool. Enroll for $29 lifetime.