# Systems Capacity Calculators

Big-O growth, RAID capacity, storage growth, latency and throughput budgets, Little's law, queueing, Erlang and SLA downtime.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://data-calc.x402tookit.com/openapi.json
- x402 manifest: https://data-calc.x402tookit.com/.well-known/x402
- Catalog (free): https://data-calc.x402tookit.com/catalog
- Health (free): https://data-calc.x402tookit.com/health
- Uptime (free): https://data-calc.x402tookit.com/uptime

## Endpoints (10)

### GET /big-o — $0.02
Compare growth classes (n, n log n, n^2, 2^n, n!) at a given n: operation counts, run time, largest n a time budget allows.
Params: n: number, opsPerSecond?: number, budgetSeconds?: number
Example: https://data-calc.x402tookit.com/big-o?n=1000&opsPerSecond=1000000000&budgetSeconds=1

### GET /capacity-planning — $0.02
Units needed for a peak load at a target utilisation plus N+k redundancy, utilisation after failures, and growth projection.
Params: peakLoad: number, capacityPerUnit: number, targetUtilizationPercent?: number, spareUnits?: integer, growthPercentPerMonth?: number, months?: integer
Example: https://data-calc.x402tookit.com/capacity-planning?peakLoad=5000&capacityPerUnit=800&targetUtilizationPercent=70&spareUnits=1

### GET /erlang-staffing — $0.02
Erlang B and C: trunks for a blocking target, or agents for a service level such as 80 percent answered in 20 seconds.
Params: trafficErlangs: number, mode?: string, targetBlocking?: number, serviceLevel?: number, answerSeconds?: number, handlingSeconds?: number
Example: https://data-calc.x402tookit.com/erlang-staffing?trafficErlangs=10&mode=b&targetBlocking=0.01

### GET /latency-budget — $0.02
Add up serial stage latencies against a target (share per stage, slack, bottleneck) and compute tail amplification from fan-out.
Params: stages: string, targetMs?: number, fanOut?: integer, percentile?: number
Example: https://data-calc.x402tookit.com/latency-budget?stages=dns%3A20%2Ctls%3A40%2Capp%3A120%2Cdb%3A60&targetMs=300&fanOut=100

### GET /littles-law — $0.02
Little's law L = rate x time in system: solve for concurrency, throughput or latency given any two; sizes pools.
Params: arrivalRate?: number, timeInSystem?: number, itemsInSystem?: number, timeUnit?: string
Example: https://data-calc.x402tookit.com/littles-law?arrivalRate=50&timeInSystem=200&timeUnit=ms

### GET /queue-model — $0.02
M/M/1 and M/M/c queue: utilisation, probability of waiting (Erlang C), queue length, wait and response time, tail odds.
Params: arrivalRate: number, serviceRate: number, servers?: integer, waitThreshold?: number
Example: https://data-calc.x402tookit.com/queue-model?arrivalRate=8&serviceRate=10&servers=1&waitThreshold=0.5

### GET /raid-capacity — $0.02
RAID 0/1/5/6/10 and ZFS RAID-Z usable capacity, efficiency, fault tolerance, write penalty and rebuild read-error risk.
Params: level: string, disks: integer, diskTb: number, spares?: integer, ureBits?: number
Example: https://data-calc.x402tookit.com/raid-capacity?level=raid5&disks=4&diskTb=4

### GET /sla-downtime — $0.02
SLA availability (99.9 percent, three nines) to allowed downtime per day, month and year; series and parallel composition.
Params: availability: number, seriesWith?: string, replicas?: integer
Example: https://data-calc.x402tookit.com/sla-downtime?availability=99.9

### GET /storage-growth — $0.02
Compound storage growth: size after N months, raw capacity with replication and overhead, months to double, months until full.
Params: current: number, growthPercentPerMonth: number, months?: integer, replication?: number, overheadPercent?: number, capacity?: number, maxUtilizationPercent?: number
Example: https://data-calc.x402tookit.com/storage-growth?current=100&growthPercentPerMonth=5&months=12&capacity=500

### GET /throughput-budget — $0.02
Requests per second times payload size to Mbps with peak factor, protocol overhead and link headroom; or IOPS to MB/s.
Params: requestsPerSecond: number, bytesPerRequest: number, peakFactor?: number, overheadPercent?: number, targetUtilizationPercent?: number, linkMbps?: number
Example: https://data-calc.x402tookit.com/throughput-budget?requestsPerSecond=1000&bytesPerRequest=100000&peakFactor=2

## Terms

Textbook formulas computed locally, provided as is. Queueing results assume Poisson arrivals and exponential service times; RAID rebuild risk uses an assumed unrecoverable read error rate; Big-O operation counts ignore constants and hardware. Use measured data for real capacity decisions, and treat results as planning estimates, not guarantees. Transfer-time, TCP window and propagation-delay maths live in the network-calc shelf and are not repeated here.