pjhtech ToolsIPv4 Subnet Calculator
Find the network, broadcast, mask and usable address range for an IPv4 prefix.
Calculator / generatorNetwork calculators & references
Calculate address ranges, packet sizes, transfer times and optical budgets. Each calculator explains its inputs and assumptions.
Plan an address space · Compare network sets · Check VPN overhead · Calculate TCP MSS · MikroTik guides · UniFi guides
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Address planning
CIDR to Netmask Converter
Convert an IPv4 prefix length into a contiguous dotted-decimal subnet mask.
Calculator / generatorNetmask to CIDR Converter
Validate an IPv4 subnet mask and recover its prefix length.
Calculator / generatorWildcard Mask Calculator
Convert between a contiguous subnet mask and its inverse ACL wildcard.
Calculator / generatorIP Range to CIDR Converter
Cover an inclusive IPv4 range with the smallest exact set of CIDR blocks.
Calculator / generatorCIDR Aggregation & Route Summarization Calculator
Aggregate IPv4 or IPv6 CIDRs exactly, or calculate a covering supernet with explicit counts of extra address space.
Calculator / generatorSubnet Splitter
Divide one IPv4 parent network into equal-size child subnets.
Calculator / generatorVLSM Calculator
Allocate different-size IPv4 LAN subnets from a parent network.
Calculator / generatorIPv6 Subnet Calculator
Calculate an IPv6 network boundary, final address and exact address-space size.
Calculator / generatorIPv6 Address Expander and Compressor
Normalize IPv6 text and inspect all eight hexadecimal groups.
Calculator / generatorReverse DNS / PTR Converter
Build IPv4 host reverse names and IPv6 host or nibble-aligned reverse-zone names.
Calculator / generatorCIDR List Comparison & Overlap Checker
Compare two IPv4 or IPv6 CIDR lists and get their exact intersection, differences, duplicates and containment relationships.
Calculator / generatorLink & transport
TCP MSS Calculator
Find the TCP MSS option value for an IP MTU, and the room left for TCP data when options are present.
Calculator / generatorMTU Budget Calculator
Find the inner IP packet size and ping data size that fit after reserving bytes for tunnel headers.
Calculator / generatorIPsec / ESP Overhead Calculator
Find how many bytes IPsec adds to your packet and the resulting IP packet size.
Calculator / generatorBandwidth and Transfer Time Calculator
Estimate file transfer duration with explicit file units and useful-throughput efficiency.
Calculator / generatorBandwidth-Delay Product Calculator
Estimate bytes in flight from bottleneck bandwidth and round-trip delay.
Calculator / generatorPackets Per Second / Line Rate Calculator
Find the Ethernet frames per second that fit a link rate, including the time used by preamble and the gap between frames.
Calculator / generatorFiber Optic Link Budget Calculator
Estimate optical path loss and spare margin from your transceiver and cable specifications.
Calculator / generatordBm / mW Converter
Convert logarithmic power in dBm to milliwatts and back.
Calculator / generatorVLAN / Ethernet Frame Overhead Calculator
Calculate Ethernet frame size, tag cost, padding and payload efficiency.
Calculator / generatorReferences
IPv4 Subnet Mask Table
One A4 page: every IPv4 prefix, mask, wildcard, address count, subnet boundaries and special-range reminders.
A4 referenceSubnetting Worked Examples
Work through original subnetting examples for boundaries, host capacity and address allocation.
A4 referenceSpecial and Private IP Address Reference
Recognize common private, shared, loopback, documentation and local address ranges.
A4 referenceCommon TCP / UDP Ports Reference
Common service ports and transport choices in a printable reference.
A4 referenceDNS Record Cheat Sheet
Understand common DNS record types, TTLs and frequent configuration mistakes.
A4 referenceIPv6 Quick Reference
A one-page A4 reference for IPv6 notation, prefix sizes, address types, multicast and reverse DNS.
A4 referenceEthernet, MTU & TCP MSS Quick Reference
A one-page A4 reference for frame size, VLAN overhead, IP MTU, TCP MSS and tunnel budgeting.
A4 referenceWi-Fi PHY Rate & Channel Width Cheat Sheet
One A4 page explaining Wi-Fi generations, channel widths, spatial streams and PHY rates without promising Internet speeds.
A4 referenceCommands for the next troubleshooting step
Once the address or packet-size calculation is complete, use the network references to test DNS, TCP, TLS and the packet path. The command guides include result interpretation and links back to the relevant calculators.
Browse network troubleshooting references