5 Free PCB Calculators for Engineers
PCB design involves a lot of math. Trace widths, via counts, impedance values, voltage drops—you could calculate all of this by hand, but why would you? The right online calculators can save you hours and prevent costly mistakes.
We've curated the five essential calculators that every hardware engineer should bookmark. All free, all useful, all frequently needed.
1. PCB Trace Width Calculator
TraceWidthCalculator.com
IPC-2221 and IPC-2152 compliant
The most fundamental PCB calculation: how wide does my trace need to be to carry X amps without overheating? This calculator answers that question using industry-standard formulas.
What It Calculates
- Trace width for your required current and temperature rise
- Cross-sectional area of the conductor
- Resistance of the trace
- Voltage drop across the trace length
- Power loss (I²R heating)
When You Need It
| Scenario | Why It Matters |
|---|---|
| Power input traces | Prevent overheating and fires |
| Motor driver outputs | Handle peak currents safely |
| Battery connections | Minimize voltage drop |
| LED driver traces | Manage thermal load |
| Any trace >500mA | Verify thermal safety |
Pro Tip: Always design for 10°C temperature rise as a default. Only go higher if you know your thermal environment can handle it. Read more in our 10 Common Trace Width Mistakes guide.
2. Via Current Calculator
Via Current Capacity Calculator
Calculate via count for power delivery and thermal management
A single via can only handle about 0.7A safely. This calculator tells you exactly how many vias you need for your power rail transitions and thermal pad connections.
What It Calculates
- Via count required for your current
- Single via capacity based on size and plating
- Thermal resistance for heat transfer applications
- Voltage drop through via transitions
When You Need It
| Application | Typical Via Count |
|---|---|
| MCU power pin | 2-4 |
| Voltage regulator input | 4-8 |
| Motor driver power | 8-16 |
| QFN thermal pad | 9-25 |
| High-power MOSFET | 16-36 |
For detailed guidance on via sizing, check out our Via Sizing Guide and Thermal Via vs Signal Via Guide.
3. PCB Impedance Calculator
Controlled Impedance Calculator
Microstrip, stripline, and differential pair calculations
High-speed interfaces like USB, HDMI, and PCIe require specific impedance values. This calculator determines the trace width needed to achieve your target impedance.
What It Calculates
- Trace width for target impedance
- Single-ended impedance (microstrip, stripline)
- Differential impedance for paired signals
- Effective dielectric constant for propagation delay
Common Impedance Targets
| Interface | Impedance | Type |
|---|---|---|
| USB 2.0/3.x | 90Ω | Differential |
| HDMI | 100Ω | Differential |
| PCIe | 85Ω | Differential |
| DDR | 40Ω SE / 80Ω diff | Both |
| Ethernet | 100Ω | Differential |
| General digital | 50Ω | Single-ended |
For complete impedance requirements by interface, see our High-Speed Impedance Guide.
4. Voltage Divider Calculator
Resistor Voltage Divider
Calculate output voltage or find resistor values
Every hardware engineer needs to level-shift signals, create reference voltages, or scale ADC inputs. A voltage divider calculator saves time picking standard resistor values.
What It Calculates
- Output voltage given input voltage and resistors
- Resistor values for desired output voltage
- Standard E-series values closest to calculated
- Current consumption and power dissipation
Common Use Cases
| Application | Example |
|---|---|
| ADC input scaling | 12V battery → 3.3V ADC range |
| Voltage reference | 5V → 2.5V for comparator |
| Level shifting | 5V logic → 3.3V input |
| Feedback networks | DC-DC regulator FB pin |
| Sensor biasing | Thermistor voltage output |
5. Decoupling Capacitor Calculator
Decoupling & Bypass Calculator
Determine capacitor values and placement
Proper decoupling is critical for stable power delivery to ICs. This calculator helps determine capacitor values based on IC requirements and target impedance.
What It Calculates
- Capacitor value for target impedance at frequency
- Self-resonant frequency including parasitic inductance
- Parallel capacitor selection for wide-band decoupling
- ESR and ESL effects on high-frequency performance
Typical Decoupling Strategy
| Frequency Range | Capacitor Type | Typical Values |
|---|---|---|
| Bulk (low freq) | Electrolytic/Tantalum | 10-100 μF |
| Mid-range | Ceramic (0805) | 1-10 μF |
| High frequency | Ceramic (0402) | 100nF |
| Very high freq | Ceramic (0201) | 10-100nF |
Bonus: Other Useful Calculators
LED Resistor Calculator
Calculate current-limiting resistor value for LEDs based on supply voltage, forward voltage, and desired current.
RC Time Constant Calculator
Determine charge/discharge time for RC circuits. Useful for timing circuits, filters, and debouncing.
Wire Gauge Calculator
Convert between AWG, mm², resistance per length, and current capacity for external wiring.
Thermal Calculator
Calculate heatsink requirements, junction temperatures, and thermal resistance paths for power components.
Electrical Box Fill Calculator
Calculate NEC-compliant box fill requirements for electrical enclosures. Essential for ensuring your PCB and wiring installations meet code requirements.
Summary: Which Calculator When?
| Task | Calculator | Link |
|---|---|---|
| Power trace sizing | Trace Width Calculator | tracewidthcalculator.com |
| Via count for power | Via Current Calculator | Via tool |
| USB/HDMI/PCIe traces | Impedance Calculator | Impedance tool |
| ADC input scaling | Voltage Divider | External |
| IC power filtering | Decoupling Calculator | External |
Try Our Free Calculators
All three of our core PCB calculators are free, with no signup required.
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