Transit Gateway Planner
Plan transit gateway attachments, routing and bandwidth across connected VPCs.
Inputs
VPCs, VPNs, and Direct Connect/ExpressRoute gateways attached
Estimated Total Monthly Cost
$10,365.00
Attachment Cost
$365.00
Data Processing Cost
$10,000.00
Total Routes (across all attachments)
200
Route Table Utilization (vs. 10,000 typical limit)
2.00%
Avg. Bandwidth per Attachment
5.000Gbps
Step by step
Values used
Number of Attachments = 10; Price per Attachment (hourly) = 0.0500; Data Processed per Month = 500,000 GB; Data Processing Price per GB = 0.0200; Average Routes per Attachment = 20; Aggregate Bandwidth Needed = 50 Gbps
Total monthly cost
cost = attachments × price_per_hr × hours_per_month + data_processed_GB × price_per_GB
Estimated Total Monthly Cost
= 10,365.00
Attachment Cost
= 365.00
Data Processing Cost
= 10,000.00
Total Routes (across all attachments)
= 200
Route Table Utilization (vs. 10,000 typical limit)
= 2.00
Avg. Bandwidth per Attachment
= 5.000 Gbps
How it works
Transit gateway planning spans three dimensions: cost (a flat hourly fee per attachment plus a usage-based fee for data actually processed — cost = attachments × $/hr × hours + data_processed_GB × $/GB), route capacity (each attachment contributes routes to a shared route table with a practical ceiling, commonly cited around 10,000 routes), and bandwidth (aggregate throughput divided across attachments, each with its own burst ceiling).
Formula
Total monthly cost
cost = attachments × price_per_hr × hours_per_month + data_processed_GB × price_per_GB
- n
- Number of attachments
- p_a
- Hourly price per attachment
- h
- Hours per month (approximately 730)
- D
- Data processed in GB
- p_d
- Price per GB processed
Frequently Asked Questions
Why does a transit gateway have a route limit?
Route tables are held in memory on the gateway's control plane and propagated to every attachment, so there's a practical ceiling (commonly around 10,000 routes per route table on major cloud platforms) to keep propagation and lookup performant at scale — large deployments should plan for route summarization rather than one route per fine-grained subnet.
How is transit gateway cost typically structured?
Most cloud providers charge a flat hourly fee per attachment (VPC, VPN, or Direct Connect/ExpressRoute) plus a separate per-GB fee for data actually processed through the gateway — cost scales with both how many things you connect and how much traffic flows between them.
When should I use route summarization?
When total routes across attachments approach the route table's practical limit, summarizing many small routes into fewer, larger aggregate routes (where addressing hierarchy allows) reduces route table pressure and keeps the gateway comfortably under its capacity ceiling.