Email Storage Calculator
Size the mailroom — users × mailbox quota plus the year's growth, checked against the plans that actually exist.
Email Storage Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Person-mailboxes only — shared and journal archives excluded
- Flat per-mailbox quotas — no per-user variance modeled
In short: 25 people on 50 GB mailboxes hold 1,250 GB on day one, and 2 MB a day of growth each adds 18 GB by month 12 — 1,268 GB against a 50 GB plan's 1,250 ceiling. Every standard plan is already past its line: Gmail's 15 GB tops at 375, Workspace's 30 at 750, Exchange's 50 at 1,250. Mail grows like compound interest on a balance nobody audits.
Formula
org GB = users × quota + users × growth × months × 30 ÷ 1,000
Mail storage is a floor plus a drift: the quota floor is users times the plan (the published lines: 15 GB consumer Gmail, 30 GB Workspace default, 50 GB Exchange standard), and the drift is retained mail per person per day — two megabytes a day is one modest attachment thread that never gets deleted. Thirty-day months keep the arithmetic honest without pretending precision the drift does not have.
Worked Example
- Enter the headcount and the plan quota each mailbox carries.
- Enter the retained-growth estimate ‒ 2 MB a day is a normal office.
- Read the org total, the plan check and the month the line breaks.
Defaults: 1,268 GB, over the 50 GB plan by 18 GB. Drive to 20 people on 40 GB with 1 MB a day and the org reads 807.2 GB against a 1,000 GB ceiling — 192.8 GB of slack, fitting with room to hire.
Strengths & Limits Of This Model
Where this engine is strong
- Checked against the plans that actually exist
- Growth priced per person per day — the drift is the finding
Where it stops
- Attachment-heavy orgs must set growth honestly
Practical Use Cases
Plan selection
which mailbox tier fits the org
Retention policy
what deleting a thread a day saves
Migration sizing
the mailroom's real footprint
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Email Storage Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What are the actual mailbox quotas?
The published lines: consumer Gmail carries 15 GB (shared with Drive and Photos), Google Workspace defaults to 30 GB and scales to 2–5 TB on higher editions, and Microsoft 365 / Exchange Online standards on 50 GB mailboxes. The presets are those three lines.
How big is a typical email?
A body-only message runs 15–100 KB — the deliverability sweet spot sits near 75 KB. Attachments are the real weight: one message caps at 20–25 MB on most providers, and Base64 encoding inflates the attachment by about a third on the wire.
Why 2 MB a day of growth?
It is a modest office: one kept attachment thread or a dozen plain mails a day. Heavy attachment cultures — contracts, scans, design files — run ten times that; the preset ladder lets you price the culture you actually have.
Why does the plan check say every plan is over?
Because quota multiplies per person and so does growth — an org whose mailboxes are genuinely full at the plan line stays full at every size. The fix is retention policy (deletion drives, archiving to cheap storage), not a bigger plan.
Does deleting mail really help at these scales?
Directly: 2 MB a day per person is 730 MB a year per mailbox. A 100-person org deleting half its retained mail halves an 86-gigabyte drift. The savings are boring, real and compounding.
Is shared-mailbox and archive space included?
No — the page prices person-mailboxes. Shared mailboxes, public folders and journaling archives bill on the same storage but sit outside the users × quota model; add them as extra 'users' if they carry real weight.
How is this different from the database size page?
That page sizes structured rows with indexes; mail is unstructured blobs with attachments and its own growth culture. The arithmetic rhymes (rows ≈ people, row size ≈ quota) but the drift dominates here in a way indexes never do.
What does archiving to cheap storage cost?
About a fifth of a dollar per terabyte-month on the coldest shelves — the S3 page prices the ladder. Archive mail past its active years and the warm mailbox stops growing while the law keeps its copy.