A megabyte (MB) is a unit of digital data equal to one million bytes, as defined by the international system of units (SI). The 1,048,576-byte unit is a mebibyte (MiB), which some software still labels MB. It sits between the kilobyte (KB) and the gigabyte (GB). Megabytes are the everyday unit for individual files such as photos, documents and attachments, and the unit where people most often mix up bytes and bits.
At a glance
- Decimal: 1 MB = 1,000,000 bytes (10^6). Binary counterpart: 1 mebibyte (MiB) = 1,048,576 bytes (2^20).
- The gap between the unit and its binary counterpart is about 4.9%.
- As a rough illustration, a smartphone photo, a typical office document with images, or a compressed music track is often a few megabytes.
- MB (megabytes) is not Mb (megabits): 1 MB = 8 Mb.
What problem it solves
The megabyte gives a convenient scale for the files people handle every day. It is also the unit in which many practical limits are set: email attachment caps, upload limits on portals and forms, message size limits in collaboration tools, and the size of software updates. Knowing the unit helps when sizing those limits and when estimating how long transfers will take.
How it works
Decimal and binary values. 1 MB = 1,000 KB = 1,000,000 bytes under SI usage. 1 MiB = 1,024 KiB = 1,048,576 bytes. Some operating systems, notably Windows, calculate in MiB but label the result MB, so the same file can show slightly different sizes in different tools.
Bytes versus bits. Storage is measured in bytes; network speed is usually measured in bits per second. A 100 Mbps internet connection can move at most about 12.5 MB per second, and real throughput is lower once protocol overhead, latency and congestion are counted. As a rough calculation, a 500 MB file takes at least 40 seconds at 100 Mbps. The glossary term Bits per Second covers network speed units in more detail.
Where megabytes appear in specifications. Cache sizes, firmware images, log file rotation thresholds and the maximum size of individual records or messages are often stated in MB.
Change rates and backups. Backup and replication tools often report how many megabytes or gigabytes changed since the last run. That change rate, not the total data size, usually determines how much bandwidth ongoing backups and replication need.
When it matters for buyers
- Sizing internet bandwidth for backups. If a backup as a service (BaaS) job needs to send several thousand MB of changes each night, convert to megabits before comparing with your circuit speed.
- Email and collaboration limits. Attachment and upload caps are usually set in MB and vary by platform and plan.
- Metered connections. Some cellular and IoT data plans still cap or price usage in MB, and overage charges add up quickly.
- Comparing speed claims. Download tools often show MB/s while providers sell Mbps; mixing them gives an eightfold error.
See our file and object storage page for how buyers compare storage services once volumes grow beyond everyday file sizes.
Questions to ask vendors
- Are your speed figures in megabits or megabytes per second, and are they sustained or peak?
- What are the attachment, upload and message size limits on each plan, in MB?
- For metered plans, how is usage rounded (per session, per KB, per MB), and what does overage cost?
- How much data does a typical daily backup or sync send across the network after the first full copy?
How it differs from a megabit (Mb)
A megabyte is a unit of stored data; a megabit is one-eighth of that and is mainly used to express network speed. Mixing them up is the most common reason transfer-time estimates are wrong by a factor of eight. A related trap is the binary mebibyte (MiB), which is about 4.9% larger than a decimal MB; the glossary term Binary Prefixes explains the binary units.