Memory Bandwidth Calculator (DDR4, DDR5, GDDR)

How it works

bandwidth (B/s) = data rate (transfers/s) × bus width (bits) ÷ 8 × channels · GB/s = bytes ÷ 10⁹, GiB/s = bytes ÷ 2³⁰ · I/O clock = data rate ÷ 2 (two transfers per clock)

DDR memory moves data on both edges of its clock, so a DDR5-6000 module performs 6,000 million transfers per second on a 3,000 MHz I/O clock. Each transfer moves the full channel width — 64 bits (8 bytes) for a DDR4 or DDR5 DIMM channel — and channels work in parallel. The result is the theoretical peak defined by the JEDEC speed grade; real copy benchmarks typically reach 70–90% of it because of refresh, bank conflicts and read/write turnarounds. Two DIMMs on the same channel do not add bandwidth.

Worked example

Dual-channel DDR5-6000: 6,000 × 10⁶ transfers/s × 64 bits ÷ 8 × 2 channels = 96 GB/s (89.41 GiB/s), or 48 GB/s per channel on a 3,000 MHz I/O clock. Reading 16 GB once therefore takes at least 166.7 ms.

Sources: JEDEC — JESD79-5 DDR5 SDRAM standard · Wikipedia — Memory bandwidth

Frequently asked questions