Email Storage Calculator
Project how much storage your email will use over years.
Include attachments; 0.1–2 MB is typical.
Results update as you type.
How it works
An email storage calculator projects how much disk or cloud space a mailbox will accumulate over time, from how many emails you receive each day, their average size, and how many years you keep them. Email quietly becomes one of the largest personal and organisational data stores, and mailbox quotas are a common source of frustration when they fill up unexpectedly, so projecting growth helps you plan capacity before you hit a limit. This estimate is useful for individuals and administrators alike. A user deciding whether a free mailbox quota will last, an IT team sizing storage for hundreds of employees, or a business setting retention policies all need to know how fast mail accumulates. Because attachments dominate size, the average message figure matters as much as the count. Seeing years of projected growth makes the case for archiving, cleanup, or a larger plan concrete rather than abstract. The calculation multiplies daily email count by average size to get megabytes per day, scales that by 365 days and the number of years, then divides by 1,024 to express the total in gigabytes. It assumes a steady arrival rate and that nothing is deleted, giving a worst-case accumulation. Real mailboxes are pruned, and average sizes shift with attachment habits, so treat the result as a planning ceiling. Individuals, administrators, and anyone managing mailboxes use an email storage calculator to forecast growth and set retention and quota policies.
storage (GB) = emails per day × average size (MB) × 365 × years ÷ 1,024
The number of emails you receive each day multiplied by the average size of each gives the megabytes accumulated daily. Multiplying by 365 extends that to a year, and by the number of years to the full period. Dividing by 1,024 converts megabytes to gigabytes. The model assumes a steady arrival rate and that mail is kept rather than deleted, giving the total space a mailbox would occupy if nothing were ever removed over the span.
Source:Standard storage accumulation model
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter emails per day, average email size and number of years.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Total storage updates instantly as you type — no button to press.
Frequently asked questions
What is a typical average email size?
A plain text email is only a few kilobytes, but most messages carry formatting, images, and signatures, and many include attachments. As a result, average sizes commonly fall between 0.1 and 2 megabytes once attachments are blended in. Business mailboxes with frequent document and image attachments trend higher. Check your mail client's storage report to find your real average, since it drives the projection far more than the raw message count.
Do attachments dominate mailbox size?
Yes, almost always. The text of an email is tiny compared with a photo, PDF, spreadsheet, or presentation attached to it. A single large attachment can outweigh thousands of plain messages. This is why average message size is such a powerful lever in the projection: a mailbox that regularly receives big attachments grows far faster than one carrying mostly text. Reducing or offloading attachments is the most effective way to control growth.
How can I reduce my email storage use?
Delete large attachments you no longer need, or save them elsewhere and remove them from the mailbox. Empty spam, trash, and sent folders regularly, as these accumulate quietly. Use search tools that sort by size to find the biggest space users. Set up archiving to move old mail off the primary quota. For organisations, retention policies that automatically expire aged mail keep storage predictable and bounded over time.
Does this assume I never delete email?
Yes, the projection assumes a steady arrival rate with nothing deleted, so it represents a worst-case accumulation if you kept every message. In practice most people delete spam, newsletters, and large attachments over time, so real mailbox size grows more slowly. Use the figure as a planning ceiling for quota and storage decisions, then adjust downward for whatever proportion of mail you realistically expect to remove or archive.
Why divide by 1,024 to get gigabytes?
The calculation works in megabytes, and in the binary convention used by most operating systems, one gigabyte equals 1,024 megabytes. Dividing the megabyte total by 1,024 converts it to gigabytes on that basis. Some providers instead use 1,000 megabytes per gigabyte, which yields a slightly larger gigabyte figure for the same data. The difference is minor for planning, but it explains small discrepancies between tools and quota displays.