IP Subnet Calculator — IPv4 Network Mask & Range Splitter
Enter any IPv4 CIDR to see full subnet details (network address, broadcast, usable hosts, subnet mask, wildcard) and optionally split the network into N equal subnets. Outputs a complete table of subnet ranges for VLAN planning, cloud VPC design, and network segmentation.
How to Use IP Subnet Calculator — IPv4 Network Mask & Range Splitter
How to Use the IP Subnet Planner:
Enter the Parent Network CIDR: Type or paste an IPv4 CIDR into the Network CIDR field. The format is an IP address followed by a slash and prefix length, such as 192.168.1.0/24 or 10.0.0.0/16. The tool auto-calculates subnet details as you type — no button press needed.
Review the Parent Subnet Details: Once a valid CIDR is entered, the Parent Subnet section shows network address, broadcast address, first and last usable host, subnet mask, wildcard mask, total IPs, and usable host count. Tags show the IP class and whether the network is private (RFC 1918) or public.
Enter a Split Count (Optional): To divide the parent network into equal subnets, type a number between 2 and 512 in the "Split into N subnets" field. The tool automatically selects the smallest prefix that can accommodate N subnets — for example, splitting a /24 into 4 subnets produces 4 × /26.
Read the Subnet Split Table: The split table lists each subnet with its CIDR, network address, first host, last host, broadcast address, and usable host count. The table header shows how many subnets are displayed versus how many are possible (since the tool rounds up to the next power of 2 and shows only the N you requested).
Copy Any Value: Hover over any address cell in the details grid and click the copy icon that appears. In the split table, click any cell directly to copy its value to the clipboard.
Use Quick Examples: Click any example button to load a preset CIDR and split count. Examples cover a home LAN ÷ 4, an office /16 ÷ 8, data centre VLANs, a Class A divided into 256 subnets, and a multi-site /20 split into sixteen /24s.
Understand the Prefix Math: When splitting into N subnets, the tool calculates bits_added = ceil(log2(N)) and adds that to the parent prefix. Three subnets requires 2 extra bits (2² = 4 possible, 3 shown). The table header always tells you the actual possible count so you know how many subnets are left unallocated.
Clear and Start Over: Click Clear to reset both inputs and start fresh with a different network.
Common Use Cases:
- VLAN planning: Divide a corporate /16 into department-sized /24 or /22 subnets.
- Cloud VPC design: Split an AWS or Azure VPC CIDR into availability zone subnets.
- Home lab setup: Divide a 192.168.0.0/24 into separate segments for devices, IoT, and servers.
- Data centre rack allocation: Allocate /27 or /28 blocks from a larger pool to server racks.
- ISP address management: Split provider blocks into customer allocations.
- Kubernetes networking: Plan pod and service CIDRs from a parent range.
- Firewall rule writing: Look up network and broadcast addresses to write accurate ACLs.
- Study and certification prep: Visualise subnet boundaries for CCNA, CCNP, or Network+ exams.
Tips and Best Practices:
- The tool rounds N up to the next power of 2 — splitting into 5 subnets uses a /3 block (8 possible), showing only 5.
- A /24 (254 hosts) is the most common LAN block; split it into 2 = two /25s (126 hosts each).
- Use the wildcard mask directly in Cisco ACLs and OSPF network statements.
- For /31 links (RFC 3021), both addresses are usable and there is no broadcast — ideal for router-to-router links.
- To create subnets of different sizes (true VLSM), run multiple calculations: first allocate the largest subnets, then use the remaining space for smaller ones.
- Private ranges (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — these are not routed on the public internet.
- When designing cloud subnets, reserve at least one subnet per availability zone plus a spare for future growth.
- The maximum displayable split is 512 subnets; for larger allocations run multiple smaller splits.
Frequently Asked Questions
Most Viewed Tools
Screen Size Converter — Diagonal Dimension Tool
Calculate screen width and height from diagonal size and aspect ratio. Convert between inches and centimeters for displays, TVs, and monitors with instant dimension calculations.
Use Tool →DPI Calculator — Print Resolution Tool
Calculate DPI (dots per inch), image dimensions, and print sizes. Convert between pixels and physical dimensions for printing and displays.
Use Tool →TOTP Code Generator — 2FA Testing Tool
Generate time-based one-time passwords from a TOTP secret key. Enter your base32 secret, choose a period and digit length, and get the current and next codes with a live countdown timer. Useful for testing and debugging 2FA integrations.
Use Tool →JSONL Formatter — Line-by-Line Validator
Format, validate, and inspect JSON Lines (JSONL) and NDJSON files. Validates each line individually, reports parse errors by line number, outputs compact JSONL or a pretty-print preview, and lets you download the cleaned file.
Use Tool →JSON to Zod — Schema Generator
Generate Zod validation schema code from a JSON sample object. Infers z.string(), z.number(), z.boolean(), z.array(), z.object(), and z.null() types automatically. Handles nested objects, arrays of objects with optional field detection, and outputs copy-ready TypeScript with import and z.infer type alias.
Use Tool →Password Entropy Calculator — Crack Time Estimator
Calculate the information-theoretic bit entropy of any password or API key. Detects character set pools automatically, shows the total number of possible combinations, and estimates crack time across five attack scenarios from rate-limited web logins to GPU cracking clusters.
Use Tool →TLS Cipher Suite Checker — Strength Analyzer
Check TLS protocol version compatibility and cipher suite strength ratings against current best practices. Supports IANA and OpenSSL cipher names — rates each suite as Strong, Weak, or Deprecated and explains why.
Use Tool →Secret Scanner — API Key & Credential Detector
Scan pasted text, code, or config files for accidentally exposed API keys, tokens, passwords, and private keys. Detects 50+ secret types across AWS, GitHub, Stripe, OpenAI, and more — all client-side, nothing leaves your browser.
Use Tool →Related DevOps & Infrastructure Tools
GitHub Actions Validator — Workflow Syntax & CI/CD Security Audit
Validate GitHub Actions workflow YAML for syntax errors, missing required fields, deprecated commands, mutable action refs, outdated action versions, and broken job dependencies. Get per-job results with fix hints in real time.
Use Tool →SSL Certificate Decoder — Expiry & SAN Inspector
Decode X.509 SSL/TLS certificates and RSA private keys in your browser. View subject, issuer, SANs, validity dates, key type, serial number, and SHA-256/SHA-1 fingerprints. Optionally check if a certificate and private key match.
Use Tool →HTTP Header Analyzer — Security & CORS Audit
Parse and analyze HTTP request or response headers. Identifies categories, explains each header, flags missing security headers, and detects duplicates or suspicious values — entirely in your browser.
Use Tool →Dockerfile Linter — Optimize & Secure Your Container Builds
Lint Dockerfile instructions for best practices, security issues, and layer optimization. Flags unpinned base images, root user, ADD vs COPY, apt-get mistakes, shell-form CMD, and more — with fix guidance for each issue.
Use Tool →Random User Agent Generator — Browser String Tool
Generate random browser user agent strings for testing and development.
Use Tool →Port Number Lookup — Common TCP/UDP Service & Protocol Database
Searchable reference for 80+ well-known TCP and UDP ports. Look up any port number or service name to see the official protocol, service description, port range (well-known/registered), and security recommendations for risky ports.
Use Tool →Cookie Parser — HTTP Cookie Decoder
Parse HTTP cookie strings into readable key-value pairs. Decode URL-encoded values and inspect cookies from browser requests.
Use Tool →Docker Compose Validator — Multi-Container YAML Syntax & Logic Check
Validate docker-compose.yml syntax, service definitions, networks, volumes, and environment variables. Catches YAML errors, broken depends_on references, missing image/build, invalid restart policies, and more — with context-aware hints.
Use Tool →Share Your Feedback
Help us improve this tool by sharing your experience