Bandwidth Calculator
Estimate how much monthly bandwidth a website or service will consume and the average link speed it implies. It is built for anyone sizing a hosting plan, CDN allowance or VPS before launch — developers, site owners and ops engineers.
How it works
The calculator multiplies three numbers:
monthly transfer = data per visit × visits per month × safety factor
Data per visit is converted to bytes using decimal SI units (1 KB = 1000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes), giving the total monthly volume. It then derives an average sustained rate by converting the monthly bytes to bits (1 byte = 8 bits) and dividing across a 30-day month (2,592,000 seconds). The optional safety factor multiplies the whole total to leave headroom for spikes.
Worked example
A page that ships 2 MB to 100,000 visitors a month, with no safety factor:
- Monthly transfer = 2 × 1,000,000 × 100,000 = 200 GB / month
- Average sustained rate = 200,000,000,000 × 8 ÷ 2,592,000 ≈ 0.62 Mbit/s
Apply a ×1.5 safety factor and the planning figure rises to 300 GB / month.
| Data per visit | Visits / month | Monthly transfer |
|---|---|---|
| 500 KB | 50,000 | 25 GB |
| 2 MB | 100,000 | 200 GB |
| 5 MB | 250,000 | 1.25 TB |
What counts as “data per visit”
Your page weight is the total bytes transferred to load one visit — HTML, CSS, JavaScript, fonts, and images combined. A lightweight blog post might weigh 200–400 KB. A marketing landing page with a hero image and tracking scripts commonly reaches 1–3 MB. A video-heavy media site can easily exceed 10 MB per visit, especially if video is auto-played rather than lazy-loaded.
To measure your actual page weight, open Chrome DevTools (Network tab), hard-reload the page with caching disabled, and read the “transferred” figure at the bottom. That number — not the “resources” figure, which includes cached assets — is what your server actually sends to each fresh visitor.
Why the average sustained rate matters
The average rate looks deceptively low. At 0.62 Mbit/s you might think any basic VPS handles it easily. But real traffic clusters in peaks: most sites receive the majority of their daily visits within a few hours. If 80% of your 100,000 monthly visits happen in 4 hours each day, that narrow window sees traffic roughly 40× the monthly average — so your actual peak link might be closer to 25 Mbit/s. The safety factor partially addresses this, but for high-traffic sites you should also consider a CDN to absorb burst demand.
Choosing a safety factor
- 1.0 — accurate only if traffic is perfectly flat, which never happens in practice.
- 1.5 — reasonable for a predictable B2B site or internal tool with known usage patterns.
- 2.0 — appropriate for consumer sites with daily peaks, weekend spikes, or occasional viral exposure.
- 3.0 or higher — warranted if you are running a launch, a product hunt campaign, or any event where traffic can spike unpredictably.
Common mistakes when estimating bandwidth
- Using cached page weight from DevTools instead of the “transferred” (uncached) value — this understates real bandwidth significantly for new visitors.
- Forgetting API calls: single-page apps can make dozens of JSON requests per visit, each adding to the transferred total.
- Ignoring crawler traffic: search engine bots and monitoring services can add 5–20% to raw byte counts on smaller sites.
All calculations run locally in your browser — nothing you enter is sent anywhere.