# PCB Trace Estimator

> Estimate trace width or current capacity Estimate copper trace width or current, resistance, voltage drop, and power loss using the IPC-2221 equation.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ohmforgepcbtraceestimator.usefulweb.site/ (interactive tool at https://ohmforgepcbtraceestimator.usefulweb.site/tool)
- JSON API: POST https://ohmforgepcbtraceestimator.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://ohmforgepcbtraceestimator.usefulweb.site/api/v1/tool)
- OpenAPI: https://ohmforgepcbtraceestimator.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://ohmforgepcbtraceestimator.usefulweb.site/mcp - tool `ohmforge_pcb_trace_estimator`

## Inputs
- mode (select): Calculate
- layer (select): Copper layer
- currentA (number): Current (used when calculating width)
- width (number): Trace width (used when calculating current)
- widthUnit (select): Width unit
- copper (number): Copper thickness
- copperUnit (select): Copper thickness unit
- temperatureRiseC (number): Allowed temperature rise above ambient
- length (number): Trace length - Used for the resistance, voltage drop and power loss estimates.
- lengthUnit (select): Length unit

## Method
- Uses the empirical IPC-2221 relation I = k × ΔT^0.44 × A^0.725, with copper cross-sectional area in square mils. The coefficient is 0.048 for external and 0.024 for internal layers.
- Solves the equation for cross-sectional area and width, or solves for current at a given width. A nominal 1 oz/ft² copper weight is converted to 0.0348 mm.
- Estimates resistance at 20 °C from copper resistivity 1.72 × 10⁻⁸ Ω·m and the specified length and area; voltage drop is I × R and power loss is I² × R.
- Flags inputs outside the IPC-2221 chart range (up to 35 A, widths up to 400 mil, 10–100 °C rise, 0.5–3 oz/ft² copper), where the curve fit is an extrapolation.

## Limits
- An empirical estimate for an isolated rectangular trace, not a fabrication design-rule check or board-level thermal analysis. Resistance, voltage drop and loss use copper resistivity at 20 °C and do not include heating, plating, vias or adjacent copper. Input limits are numerical safeguards, not a validated operating range; verify the finished copper thickness and design with your fabricator.