Data Storage Unit Converter (B/KB/MB/GB/TB)
Enter any storage size and see every common unit at once — B, KB, MB, GB, TB, PB (decimal, used by drive manufacturers and networking) alongside KiB, MiB, GiB, TiB, PiB (binary, used by your OS). The instant answer to the perennial "why does my 1 TB drive show as 931 GB?" question.
Please enter a valid number
Decimal (SI · 1000-base)
Drive labels, network specs and bandwidth
Binary (IEC · 1024-base)
Operating systems, RAM and addressable capacity
Tip: a 500 GB drive shows ~465 GiB in Windows — not missing capacity, just different bases. Manufacturers use 1 GB = 10⁹ (SI); OSes use 1 GiB = 2³⁰ (IEC). And 100 Mbps internet ≈ 12.5 MB/s download (÷ 8) — bits vs bytes.
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Formula
Decimal (SI): 1 KB = 10³ B, 1 MB = 10⁶ B, 1 GB = 10⁹ B, 1 TB = 10¹² B Binary (IEC): 1 KiB = 2¹⁰ B = 1024 B, 1 MiB = 2²⁰ B, 1 GiB = 2³⁰ B, 1 TiB = 2⁴⁰ B
- · Conversions follow IEC 80000-13:2008: Ki / Mi / Gi / Ti / Pi are binary (× 1024); K / M / G / T / P are decimal (× 1000).
- · Hard drives, SSDs, USB sticks, SD cards and bandwidth specs (e.g. "500 GB", "1 Gbps") all use the decimal SI prefixes — the units stamped on the box.
- · Windows and older macOS (pre-10.6) report "GB" while actually meaning GiB (2³⁰ B), so a 1 TB drive shows as ~931 "GB" — roughly 6.9% smaller. macOS 10.6+ and most modern Linux distros now display true SI gigabytes.
- · RAM, CPU cache and flash memory chips are physically wired in powers of two — so "8 GB of RAM" is really 8 × 2³⁰ B = 8 GiB ≈ 8.59 GB (SI).
- · "Mbps" is megabits per second; divide by 8 to get megabytes per second — 100 Mbps ≈ 12.5 MB/s peak download (before protocol overhead).
- · 1 PB = 1000 TB; cloud providers (AWS, Google, Meta) routinely talk in PB and even EB (10¹⁸ B) at the data-centre level.
- · Sources: IEC 80000-13:2008 §3-12 and §3-13; NIST SP 811 Table 5.
Frequently asked
Why does my brand-new 1 TB drive show as only 931 GB in Windows?
No capacity is missing — the two "GB" are different units. Drive manufacturers use decimal SI: 1 TB = 10¹² bytes = 1,000,000,000,000 B. Windows uses binary IEC values but still labels them "GB": 1 "GB" = 2³⁰ B = 1,073,741,824 B. So 10¹² ÷ 2³⁰ ≈ 931.32 — your 1 TB drive measures as 931 GiB in Windows units. Same story: a 256 GB SSD ≈ 238 GiB, 500 GB ≈ 465 GiB, 2 TB ≈ 1.82 TiB. Every byte you paid for is there; the ruler is different.
How big is the gap between "GB" and "GiB" in practice? Does it matter?
The gap compounds with each prefix: KB vs KiB = 2.4% (1024 / 1000); MB vs MiB = 4.86%; GB vs GiB = 7.37%; TB vs TiB = 9.95%; PB vs PiB = 12.59%. The larger the unit, the wider the divergence — that 1 TB drive "missing 70 GB" feels alarming but is just the 1024-base ruler talking. For everyday use it does not matter, but backup planning, server provisioning, bandwidth billing and cloud-storage quotas all need clarity about which family is being charged — otherwise you can over- or under-pay.
My ISP says 100 Mbps but downloads max out at ~12 MB/s — why?
Mbps is megabits per second, not megabytes — 1 byte = 8 bits, so divide by 8. 100 Mbps ÷ 8 = 12.5 MB/s, which is exactly what you are getting. Add 5–10% TCP/HTTP protocol overhead and server-side rate limits, and 11–12 MB/s is a healthy real-world result. Networking has always used bits (the number looks bigger in ads) while files and drives are measured in bytes — putting the two side by side is what trips people up. The next time you see "1 Gbps fibre", remember the ceiling is ~125 MB/s download, not 1 GB/s.
Is "8 GB of RAM" 8 GB (SI) or 8 GiB (binary)?
It is 8 GiB — that is, 8 × 2³⁰ = 8,589,934,592 bytes ≈ 8.59 GB (SI). Because RAM chips are addressed by physical address lines, sizes must be a power of two: 4, 8, 16, 32 GiB and so on; an "8.00 GB (SI)" stick would be physically impossible. Vendors still label them "GB" as a long-standing (strictly incorrect) convention. So a "16 GB" stick really holds 16 GiB ≈ 17.18 GB (SI), which is why `free -h` on Linux defaults to GiB.
Which family is "correct" — should I use GB or GiB?
Both are correct — context determines which to use. The international standards (IEC 80000-13 and NIST SP 811) are explicit: K / M / G / T / P always mean powers of 10 (SI); Ki / Mi / Gi / Ti / Pi mean powers of 2 (IEC). If you mean 1024, write KiB — never "KB (1024)". In practice the industry still mixes them: drives, network speeds and cloud storage use SI; operating systems, RAM and a lot of older IT literature use binary values but label them SI. To avoid ambiguity: (1) use GiB / MiB whenever you mean a power-of-two number; (2) use GB / MB when quoting manufacturer labels; (3) when unsure, show both — exactly what this tool does.
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