Cloud NAT Calculator
Size Cloud NAT ports and addresses from VM count and price gateway uptime plus per-GB data processing.
About Cloud NAT Calculator
Cloud NAT reserves a fixed block of source ports per VM up front rather than allocating them on demand, so the address requirement is purely arithmetic: total reserved ports divided by the 64,512 ports each NAT IP provides. The billing is separate again — gateway uptime scales with VM count and data processing is charged per GB in both directions. The default 64 ports per VM is fine for a web server and hopeless for a crawler or a service that opens hundreds of connections to one API endpoint, and exhaustion shows up as intermittent connection timeouts rather than a clear error. Confirm the current uptime tier and per-GB processing price in the Google Cloud pricing calculator.
Formula
Cloud NAT
NAT addresses = ceil(VMs × ports per VM ÷ 64,512); cost = VMs × uptime price × hours + GB processed × data price + addresses × address price × hours.
- ports per VM
- Source ports Cloud NAT reserves per VM, 64 by default
- 64,512
- Usable source ports each NAT IP address provides
- port headroom
- Gap between reserved ports and the observed peak connections to one destination
Worked example
With the default values below, Cloud NAT Calculator returns Monthly Cost of $224.53. Change any input above and every figure here is recalculated in your browser.
Inputs used
- VMs behind the gatewayaccepts 1–100,000 VMs
- 40 VMs
- Ports reserved per VMaccepts 32–65,536 ports
- 64 ports
- Usable ports per NAT addressaccepts 1,024–65,536 ports
- 64,512 ports
- Gateway uptime price per VM-houraccepts 0–10 USD/VM-hour
- 0.0014 USD/VM-hour
- Data processed through NATaccepts 0–10,000,000 GB
- 4,000 GB
- Data processing price per GBaccepts 0–10 USD/GB
- 0.045 USD/GB
- In-use external address price per houraccepts 0–10 USD/hour
- 0.005 USD/hour
- Hours in the billing monthaccepts 1–744 hours
- 730 hours
- Peak connections per VM to one destinationaccepts 1–65,536 connections
- 48 connections
Results
- Monthly Cost
- $224.53
- NAT Addresses Required
- 1 addresses
- Gateway Uptime Charge
- $40.88
- Data Processing Charge
- $180.00
- External Address Charge
- $3.65
- Total Ports Allocated
- 2,560 ports
- Port Headroom per VM
- 25.0%
- Port Exhaustion Risk
- Low — comfortable port headroom for the observed peak
Step by step
- 1Values used
- 2Cloud NAT
- 3Monthly Cost= 224.53
- 4NAT Addresses Required= 1 addresses
- 5Gateway Uptime Charge= 40.88
- 6Data Processing Charge= 180.00
- 7External Address Charge= 3.65
- 8Total Ports Allocated= 2,560 ports
Assumptions and limits
- The result is derived only from the 9 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Cloud NAT calculated?
NAT addresses = ceil(VMs × ports per VM ÷ 64,512); cost = VMs × uptime price × hours + GB processed × data price + addresses × address price × hours. Cloud NAT reserves a fixed block of source ports per VM up front rather than allocating them on demand, so the address requirement is purely arithmetic: total reserved ports divided by the 64,512 ports each NAT IP provides. The billing is separate again — gateway uptime scales with VM count and data processing is charged per GB in both directions.
Why does Cloud NAT matter?
The default 64 ports per VM is fine for a web server and hopeless for a crawler or a service that opens hundreds of connections to one API endpoint, and exhaustion shows up as intermittent connection timeouts rather than a clear error. Confirm the current uptime tier and per-GB processing price in the Google Cloud pricing calculator.
What values do I need to enter?
This calculator takes 9 inputs: VMs behind the gateway, Ports reserved per VM, Usable ports per NAT address, Gateway uptime price per VM-hour, Data processed through NAT, Data processing price per GB, In-use external address price per hour, Hours in the billing month, Peak connections per VM to one destination. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why do ports run out when the VM has plenty of sockets?
Cloud NAT ports are consumed per unique destination tuple, so 64 ports means 64 simultaneous connections to the same destination address and port — not 64 connections in total. Raising the minimum ports per VM, or enabling dynamic port allocation, is the fix.