Free Modbus Tools
15 free online calculators, converters, and decoders for Modbus engineers and technicians. No signup required — use them directly in your browser.
RTUTCPConverterCalculatorDecoderReferenceGuide
RTU
Modbus CRC Calculator
Calculate CRC-16 checksum for Modbus RTU frames. Enter hex bytes and get the correct CRC instantly with full frame preview.
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TCP
Modbus TCP Packet Builder
Build a valid Modbus TCP MBAP + PDU packet. Fill in Unit ID, Function Code, address, and data — get the hex frame instantly.
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Address
Modbus Register Calculator
Convert between PLC-style addresses (40001) and zero-based register numbers. Identifies register type and function code to use.
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Converter
Modbus Data Type Converter
Convert raw Modbus register values to INT16, UINT16, INT32, FLOAT32, and more. Supports Big Endian and Little Endian byte order.
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Decoder
Modbus Hex Frame Decoder
Paste a raw Modbus RTU or TCP hex frame and decode every field with labels — Unit ID, FC, address, data, CRC validation.
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RTU
Baud Rate Calculator
Calculate Modbus RTU bit timing, frame duration, and maximum poll rate for any baud rate and serial configuration.
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Reference
Function Code Reference
Complete searchable reference for all Modbus function codes. Expand each FC for request/response format and register limits.
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Decoder
Exception Code Decoder
Look up any Modbus exception code (01–0B) and get a plain English explanation, likely causes, and how to fix it.
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Converter
Float to Register Converter
Convert IEEE 754 floating point numbers to two 16-bit Modbus registers and back. Shows all byte order configurations.
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Converter
Byte Order / Endian Converter
Swap byte and word order for Modbus register values. Convert between Big Endian, Little Endian, Word Swap, and Byte Swap.
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Calculator
Modbus Scaling Calculator
Convert raw Modbus register values to engineering units. Supports min/max scaling and gain + offset mode for sensors.
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Converter
Binary / Hex / Decimal Converter
Convert numbers between Binary, Hexadecimal, Decimal, and Octal instantly. Supports 16-bit and 32-bit modes.
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RTU
RS-485 Cable Length Calculator
Find the maximum RS-485 cable length for your baud rate. Includes termination resistor guidance and cable type recommendations.
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Guide
Unit ID / Slave ID Finder
Step-by-step interactive guide to find the Modbus Unit ID of any device. Covers manuals, defaults, DIP switches, and brand tips.
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Calculator
Modbus Poll Time Calculator
Calculate how long it takes to poll N Modbus registers at a given baud rate. Optimize your scan cycle for real-time control.
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Scanner
Modbus Unit ID & Port Scanner
Scan a range of unit IDs (1–247) and ports to discover which Modbus TCP devices respond. Uses FC03 at address 0 — the same method as ModPackQT Master.
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Energy & Solar Calculators
Coming SoonFree sizing calculators for off-grid solar, battery banks, and DC wiring — built for engineers and installers.
☀️
Solar PV System Sizing
Panels, battery kWh, and inverter size for any load and sun hours.
Preview →
🔋
Off-Grid Battery Bank Sizing
Days of autonomy, kWh, and series/parallel config for any battery.
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📈
Solar ROI & Payback
Payback period, 25-year savings, NPV, and CO₂ offset.
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⚡
Inverter Sizing
Right inverter rating from your appliance list with surge headroom.
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DC Wire & Cable Sizing
Correct AWG/mm² gauge for voltage drop and power loss.
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🧮
Battery SOH Predictor
State-of-health, end-of-life year, and levelised cost for LFP, NMC, and more.
Preview →
Ready to connect real Modbus devices?
ModPackQT is a free Modbus Master and Slave Simulator — connect to PLCs, energy meters, and VFDs directly in your browser.
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