Why 1.5 GB turns into 1.4 GB on Windows
The calculator opens on a 25 minute screen recording. A Mac or a phone lists the file at 1.5 GB. Copy the same file to a Windows laptop and Explorer reports about 1.4 GB. No data went missing. Two counting systems share the same letters.
Drive makers, macOS since Snow Leopard, iOS, and Android count in thousands. One GB there is 1,000,000,000 bytes. Windows counts in powers of 1,024 and still prints GB. Its gigabyte holds 1,073,741,824 bytes, so the same file looks smaller.
| Printed on the box | Windows reports | Gap |
|---|---|---|
| 64 GB phone or USB stick | 59.6 GB | 6.9% |
| 256 GB SSD | 238.42 GB | 6.9% |
| 512 GB SSD | 476.84 GB | 6.9% |
| 1 TB drive | 931.32 GB | 6.9% |
| 2 TB drive | 1.82 TB | 9.1% |
| 4 TB drive | 3.64 TB | 9.1% |
The gap grows with each unit. Kilobytes differ by 2.3%, megabytes by 4.6%, gigabytes by 6.9%, terabytes by 9.1%. Free space on a new drive drops lower still, because formatting reserves room for the file system and most laptops ship with a recovery partition.
Linux splits the difference. ls -lh and du -h count in 1,024 and print a single letter, so the recording shows as 1.4G. df -H and the GNOME Files window count in 1,000. Add --si to du or ls for decimal output.
The names KiB, MiB, and GiB exist for the 1,024 versions. Windows never adopted them. The calculator prints the GiB figure under the two readings, so a spec sheet written in GiB matches up without guesswork.
The limits behind the fit check
Each row compares your size with a published cap. Where a service says 25 MB and never states the base, the check uses the smaller decimal reading. A file passing here passes there.
| Limit | Bytes used | What happens over the cap |
|---|---|---|
| Gmail | 25,000,000 | Counts every attachment in one email. Gmail offers a Google Drive link instead. |
| Outlook.com | 20,000,000 | Counts the whole email. Outlook offers a OneDrive link instead. |
| Discord, free | 10,000,000 | Upload refused. Nitro raises the cap. |
| GitHub | 104,857,600 | Push rejected. Warnings start at 50 MiB. Git LFS handles bigger files. |
| WhatsApp document | 2,000,000,000 | Send refused. Videos sent as media get recompressed, so send as a document to keep the original. |
| FAT32 | 4,294,967,295 | Copy fails with a "file too large" error even on a near-empty stick. Format the stick as exFAT. |
| CD-R, 80 min | 737,280,000 | Burning software asks for a second disc. |
| DVD+R | 4,700,372,992 | DVD-R holds a few megabytes more. The check uses the smaller disc. |
| BD-R, single layer | 25,025,314,816 | Dual layer discs hold 50 GB. |
Email shrinks the cap further
Attachments travel as Base64 text, which turns every 3 bytes into 4 characters. A 20 MB file leaves your outbox as about 26.7 MB of message. Gmail and Outlook.com check the raw file in their web apps. A company mail server set to a 25 MB message limit checks the encoded message, so files above about 18.7 MB bounce. The encoded size under each email row tells you where you stand.
Service caps change. The figures above were set in October 2026. Check the service's help page before a deadline rides on the answer.
Sizing a recording before you press record
Media size follows one rule: bitrate times length. Bitrates come in bits per second and files in bytes, so divide by 8 at the end.
bytes = bits per second × seconds ÷ 8- 25 minute 1080p recording at 8 Mbps. 8,000,000 × 1,500 ÷ 8 = 1,500,000,000 bytes. The 1.5 GB sample above.
- 4 minute song at 320 kbps. 320,000 × 240 ÷ 8 = 9,600,000 bytes, or 9.6 MB. Fine for Gmail, too big for free Discord.
- One minute of CD-quality WAV. 44,100 samples × 2 bytes × 2 channels × 60 = 10,584,000 bytes. A 45 minute album comes to 476 MB and fits on one CD-R.
- A 12 MP photo held as raw pixels. 4,032 × 3,024 × 3 bytes = 36,578,304 bytes. The JPEG or HEIC on your phone weighs a few megabytes, because compression throws away detail you would not notice.
The video chips use YouTube's recommended upload bitrates for standard dynamic range: 5 Mbps for 720p, 8 for 1080p, 12 for 1080p at 60 fps, and around 40 for 4K. Most encoders use a variable bitrate, so treat the estimate as a target. When the number has to be close, record a 30 second test clip, read its size, and scale up.
Mbps on the speed test, MB on the file
Connection speeds count megabits. File sizes count megabytes. One byte is eight bits, so a 100 Mbps line moves 12.5 MB per second at best.
Home plans upload far slower than they download. Picture a plan sold as 300 Mbps with 20 Mbps up. The 1.5 GB recording takes 10 minutes to reach a cloud folder, not the 40 seconds the headline speed suggests. Type your upload figure into the speed box for an honest number.
Real transfers finish later than the line rate. Protocol overhead eats a few percent. Wi-Fi, a VPN, or a housemate streaming 4K eats more.
Totals for a folder full of files
Pick a folder or drag one onto the drop area and every subfolder gets counted. The browser reads each file's size from the file system listing and never opens the contents. A 40 GB folder of video totals as fast as a folder of notes, and nothing leaves your computer.
The breakdown shows which file types hog the space and lists the 100 largest files with their folder path. The CSV download holds every file, for sorting in a spreadsheet. Per-file limits such as FAT32 and GitHub get checked against each file, so the fit list tells you how many files break the rule, not only whether the total does.
What this calculator leaves out
- Size on disk. Files fill whole clusters. NTFS uses 4 KiB clusters by default, so a 200 byte config file takes 4,096 bytes of disk. A folder of 50,000 tiny files needs far more room than its total. The figures here match the Size line in Windows Properties, not Size on disk.
- Zipped size. Text, CSV, and log files shrink to a fraction when zipped. JPEG, MP4, MP3, and existing ZIP files barely shrink, since they are compressed already. Zipping a photo folder to squeeze under an email cap rarely works.
- Container overhead. Media estimates count the audio and video streams. MP4 and MKV add an index and metadata, usually well under 1% of a long file.
- Folder drops in older browsers. Dragging a folder needs a current Chrome, Edge, Firefox, or Safari. If a drop adds nothing, use Pick a folder.
- Huge folders. Six-figure file counts take a few seconds to list. The table stays capped at 100 rows to keep the page responsive.