Disk Size and Partition Converter
ConvertEverything runs locally in your browser — nothing is uploaded
Two questions answered at once: why a 500GB drive shows 465GB, and how many MB to enter to get a 100GB partition. That 7% is a base difference, not missing capacity. Drive vendors count in base 10 (500 GB = 500,000,000,000 bytes) while the operating system displays in base 2 (÷1024³ = 465.66). Strictly, the OS figure is GiB and the vendor figure is GB — one word shared by two bases, which makes it look like shrinkage. This tool puts both side by side. ⚠️ No “magic number for whole-GB partitions”. Formulas like “enter 102407 MB for exactly 100GB” circulate on forums, but that remainder comes from filesystem metadata (the NTFS MFT, root directory entries), which depends on cluster size and file count — the same number differs between 4K and 64K clusters. Publishing an exact-looking constant would present one person’s drive at one cluster size as a general rule. What is given here is the step that can be computed exactly: enter N×1024 MB and the partition itself is N GiB; after formatting it shows slightly less, by an amount the filesystem decides.
Features
- Three modes: wanted GB → MB to enter, entered MB → what shows, and a marketed-vs-shown table
- Shows both GiB and the byte count, so the base difference is visible
- The table covers common capacities from 256GB to 16TB
- ⚠️ No invented “magic number” — instead it explains that the shortfall is filesystem metadata and depends on cluster size
- Extreme inputs are clamped rather than producing absurd numbers
- Computed locally
How to use
- Pick what you want worked out (usually the first)
- Enter the size and the base (1024 for an operating system)
- The MB to enter and the byte count appear immediately
- Switch to the table mode to see why capacity “goes missing”
FAQ
- My 500GB drive shows 465GB. Was I short-changed?
- No. Two bases share one unit name: vendors count in base 10 (500 GB = 500 × 1000³ = 500,000,000,000 bytes) while the OS displays in base 2 (÷1024³ = 465.66). Strictly the OS figure should be called GiB, but Windows has always written GB — so the same capacity looks 6.9% smaller. Every capacity follows this ratio; a 1TB drive showing 931GiB is the same thing.
- How many MB should I enter for a 100GB partition?
- Enter 102400 MB (100 × 1024) and the partition is exactly 100 GiB. After formatting, the OS will show slightly less — the filesystem keeps some for metadata (the NTFS MFT, root directory entries), and how much depends on cluster size and file count. The “enter 102407 for exactly 100” advice found on forums was measured on one machine at one cluster size, so no such constant is given here.
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