# PCB Trace Resistance and Voltage Drop Calculator

> Source: https://netray.co/tools/pcb-trace-resistance-voltage-drop-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Compute DC resistance, voltage drop and I squared R loss for a copper trace including the temperature coefficient of copper.

## Category

electronics

## Industry

Electronics Manufacturing

## Audience

- PCB design engineer
- Power electronics engineer
- Hardware engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Trace length

**Key:** len

**Type:** number

**Default:** 100

**Min:** 0

**Step:** 1

**Unit:** mm

#### Trace width

**Key:** w

**Type:** number

**Default:** 0.5

**Min:** 0.05

**Step:** 0.05

**Unit:** mm

#### Copper weight

**Key:** oz

**Type:** select

**Default:** 1

**Options:**

##### 0.5 oz

**Value:** 0.5

##### 1 oz

**Value:** 1

##### 2 oz

**Value:** 2

##### 3 oz

**Value:** 3

#### Operating copper temperature

**Key:** temp

**Type:** slider

**Default:** 25

**Min:** -40

**Max:** 125

**Step:** 1

**Unit:** C

#### Current

**Key:** amps

**Type:** number

**Default:** 1

**Min:** 0

**Step:** 0.1

**Unit:** A

**Outputs:**

#### Copper thickness

**Key:** t_mm

**Expr:** oz * 0.035

**Format:** decimal

**Description:** mm, nominal.

#### Resistance at 20 C

**Key:** r20

**Expr:** 0.00001724 * len / (w * t_mm)

**Format:** decimal

**Description:** Ohms, using 1.724e-8 ohm m resistivity.

#### Resistance at operating temperature

**Key:** r

**Expr:** r20 * (1 + 0.00393 * (temp - 20))

**Format:** decimal

**Primary:** true

**Description:** Ohms, with copper temperature coefficient 0.00393 per C.

#### Voltage drop

**Key:** vdrop

**Expr:** amps * r

**Format:** decimal

**Primary:** true

**Description:** Volts.

#### Power loss

**Key:** loss

**Expr:** amps * amps * r

**Format:** decimal

**Description:** Watts.

**Chart:**

#### Trace resistance vs width

**Type:** line

**X:** w

**From:** 0.1

**To:** 3

**Steps:** 30

**Series:**

- r

**Disclaimer:** Uses nominal copper thickness and DC resistance. Etch tolerance, plating variation and skin effect at high frequency change real resistance.

## Content

**Intro:** Long power traces drop voltage and waste power as heat. This calculator gives DC resistance, voltage drop and loss for a copper trace so you can decide on width, weight or a plane before the layout is frozen.

**Sections:**

#### How to use it

**Body:** Enter the length and width of the trace and choose the copper weight. Set the expected copper temperature, since resistance rises with heat, and the load current. The tool returns resistance at 20 C and at temperature, voltage drop and power loss. Use the chart to see how much resistance falls as width increases.

#### The formula behind it

**Body:** Resistance equals resistivity times length divided by cross-sectional area. Copper resistivity is about 1.724e-8 ohm meters at 20 C, which is 1.724e-5 ohm mm. Thickness is copper ounces times 0.035 mm. Temperature correction multiplies by one plus 0.00393 times the difference from 20 C.

**Bullets:**

- R equals rho x L / (w x t)
- Voltage drop is current times resistance
- Loss is current squared times resistance

#### Reading the result

**Body:** A 100 mm long, 0.5 mm wide 1 oz trace measures about 0.1 ohm at 20 C. At 1 A that drops roughly 0.1 V, which matters on a 3.3 V rail and almost nothing on a 24 V rail. Heat raises resistance, so at 85 C the same trace is about 25% higher.

#### Common mistakes

**Body:** Ignoring the return path doubles the real drop, since ground current also flows through copper. Another mistake is counting only trace length and forgetting vias, connector contacts and solder joints, each of which adds milliohms. Add those from datasheets for a full budget.

**Cta:** Netray can help tie design calculations and engineering change approvals into your ERP so released PCB revisions are traceable.

**Faq:**

#### What is the resistance per square of 1 oz copper?

**Answer:** About 0.5 milliohm per square at 20 C. Resistance equals this value times length divided by width, which is a quick mental check for any trace.

#### Does this include skin effect?

**Answer:** No. It is a DC calculation. At high frequency skin depth and roughness raise the effective resistance, which needs a field solver.

#### How does temperature affect copper?

**Answer:** Resistance rises roughly 0.39% per degree C. At 100 C, copper has about 31% more resistance than at 20 C.

#### Should I use the final plated copper thickness?

**Answer:** Outer layers gain plating, so finished copper is thicker than the base foil. Use the fabricator's finished thickness for accuracy and the nominal value for a safe estimate.

## Search terms

pcb trace resistance calculator, pcb voltage drop calculator, copper trace resistance, trace resistance by copper weight, pcb power loss trace, milliohm per square copper, pcb track resistance, trace voltage drop current

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