What the WebSocket Connection Cost Calculator measures
WebSocket connections are long-lived — unlike a typical HTTP request that opens, responds, and closes in milliseconds, a WebSocket stays open for the length of a chat session, a live dashboard view, or a multiplayer game round. That changes how hosting cost scales: instead of paying per request, you're effectively paying for connection-minutes held open plus the messages sent over them. This calculator turns three usage numbers — how many connections you expect at once, how long the average one stays open, and how many messages flow per minute — into an estimated monthly infrastructure cost, split into a connection-holding cost and a message-throughput cost.
It's meant for early capacity planning: sizing a WebSocket-based feature (live chat, real-time notifications, collaborative editing, a multiplayer lobby, or a trading ticker) before you commit to a hosting tier or a per-connection pricing plan from a managed WebSocket provider. Because the per-unit rates are simplified defaults, treat the output as a comparative estimate for choosing between usage scenarios, not as a quote you can hand to finance — always check your actual host or provider's published pricing for the real per-connection and per-message rates.
The formula and its variables
Connection Cost = Connections × $0.0001 × Duration (min); Message Cost = Connections × Messages/min × Duration (min) × $0.000001; Total = Connection Cost + Message Cost.
- Concurrent Connections: how many WebSocket connections are open at the same time during the period you're costing out.
- Avg Duration (min): the average number of minutes a single connection stays open.
- Messages/Min: the average number of messages sent or received per connection, per minute.
- Connection Cost: models the cost of simply holding connections open, independent of how much data flows through them.
- Message Cost: models the additional cost driven by message volume, which scales with connections, duration, and messages per minute all at once.
Worked example
Using the placeholder values — 1,000 concurrent connections, 60 minutes average duration, 10 messages per minute — the connection cost is 1,000 × 0.0001 × 60 = $6.0000. The message cost is 1,000 × 10 × 60 × 0.000001 = $6.0000 as well (600,000 total messages × $0.000001). Total cost comes to $12.0000. If you double the message rate to 20 messages per minute, only the message cost changes: 1,000 × 20 × 60 × 0.000001 = $12.0000, pushing the total to $18.0000 — a reminder that chatty applications (frequent small updates) scale cost faster than simply having more idle connections open.
Common mistakes and how to interpret the result
- Entering a single session's duration when you meant total monthly connection-minutes, or vice versa — decide whether "duration" means one typical session or a cumulative period, and stay consistent since the model multiplies it directly into both cost terms.
- Forgetting that the default rates ($0.0001 per connection-minute and $0.000001 per message) are illustrative defaults, not any specific vendor's real pricing — replace them conceptually with your actual provider's published rates before budgeting.
- Ignoring peak versus average concurrency. If connections spike during specific hours (e.g., a live event), run the calculator with your peak concurrent count too, since infrastructure often has to be provisioned for the peak, not the average.
- Treating message cost as negligible. As the worked example shows, a high-frequency, low-connection-count app can rack up message cost that rivals or exceeds the connection-holding cost.