---
title: "Calculate PCB microstrip trace width for a target characteristic impedance using the Hammerstad-Jensen closed-form equations. Given target impedance (Z0), substrate dielectric constant (er), substrate height, and copper weight, returns the required trace width and effective dielectric constant. Optionally computes effective wavelength at a given frequency. Essential for RF PCB layout to achieve controlled impedance traces (e.g. 50 ohm for SMA connectors). References IPC-2141."
method: POST
path: "/api/microstrip"
tags: ["rf"]
---

# Calculate PCB microstrip trace width for a target characteristic impedance using the Hammerstad-Jensen closed-form equations. Given target impedance (Z0), substrate dielectric constant (er), substrate height, and copper weight, returns the required trace width and effective dielectric constant. Optionally computes effective wavelength at a given frequency. Essential for RF PCB layout to achieve controlled impedance traces (e.g. 50 ohm for SMA connectors). References IPC-2141.

`POST /api/microstrip`

## Request

- Base URL: `https://calc.engineer`
- URL: `https://calc.engineer/api/microstrip`
- Auth: none declared

## Request body

- object
  - `z0_ohm` number: Target characteristic impedance in ohms (default 50)
  - `er` number: Substrate relative dielectric constant (default 4.6 for FR-4)
  - `height_mm` number, required: Substrate height (dielectric thickness) in millimetres
  - `copper_oz` number: Copper weight in oz/ft2 (1 oz = 0.035 mm thickness)
  - `freq_mhz` number: Optional frequency in MHz for effective wavelength calculation

## Response `200`

Computed result for microstrip

- object
  - `result` object, required
    - `width_mm` number, required: Required trace width in millimetres
    - `er_eff` number, required: Effective dielectric constant of the microstrip
    - `wavelength_eff_mm` number, nullable, required: Effective wavelength in millimetres at the given frequency (null if freq not provided)
  - `tool` string, required
  - `version` string, required
  - `computed_at` string, date-time, required
  - `chain` object, required
    - `feeds` unknown[]
      - unknown
    - `accepts_from` unknown[]
      - unknown

## Other responses

- `400`: Validation error or invalid JSON
- `404`: Tool not found

---

[API](https://skmtc.dev/calc/apis/calc-engineer-api.md) · [All operations](https://skmtc.dev/calc/apis/calc-engineer-api/llms.txt) · [OpenAPI document](https://skmtc.dev/calc/apis/calc-engineer-api/revisions/8830480ec488?raw)