# PCB Trace Current Capacity and Temperature Rise Calculator > Source: https://netray.co/tools/pcb-trace-current-capacity-temperature-rise-calculator > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Enter trace width, copper weight, layer type and allowed temperature rise to get the maximum current from the IPC-2221 equation. ## Category electronics ## Industry Electronics Manufacturing ## Audience - PCB design engineer - PCBA process engineer - Hardware engineer ## Tool **Kind:** calculator **Inputs:** #### Trace width **Key:** width_mm **Type:** number **Default:** 1 **Min:** 0.05 **Step:** 0.05 **Unit:** mm **Help:** Finished copper width of the trace. #### Copper weight **Key:** oz **Type:** select **Default:** 1 **Options:** ##### 0.5 oz (17.5 um) **Value:** 0.5 ##### 1 oz (35 um) **Value:** 1 ##### 2 oz (70 um) **Value:** 2 ##### 3 oz (105 um) **Value:** 3 #### Layer type **Key:** k **Type:** select **Default:** 0.048 **Options:** ##### External (outer layer) **Value:** 0.048 ##### Internal (inner layer) **Value:** 0.024 **Help:** Inner layers shed heat poorly, so IPC-2221 uses a smaller constant. #### Allowed temperature rise **Key:** dt **Type:** slider **Default:** 20 **Min:** 5 **Max:** 100 **Step:** 1 **Unit:** C **Help:** Rise above ambient, not absolute temperature. **Outputs:** #### Copper thickness **Key:** thick_mil **Expr:** oz * 1.378 **Format:** decimal **Description:** In mil. 1 oz copper is about 1.378 mil. #### Trace width **Key:** width_mil **Expr:** width_mm / 0.0254 **Format:** decimal **Description:** In mil. #### Cross section **Key:** area **Expr:** width_mil * thick_mil **Format:** decimal **Description:** Square mil. #### Maximum current **Key:** imax **Expr:** k * pow(dt, 0.44) * pow(area, 0.725) **Format:** decimal **Primary:** true **Description:** Amps for the selected temperature rise (IPC-2221 equation). #### Current density **Key:** density **Expr:** imax / (width_mm * oz * 0.035) **Format:** decimal **Description:** Amps per square mm of copper. **Chart:** #### Maximum current vs trace width **Type:** line **X:** width_mm **From:** 0.2 **To:** 5 **Steps:** 30 **Series:** - imax **Disclaimer:** IPC-2221 curves are an approximation for isolated traces. Planes, vias, nearby heat sources, airflow and board thickness change real temperature rise. Verify with a thermal test or the current IPC-2152 data for critical designs. ## Content **Intro:** This calculator answers the question every layout review asks: how much current can this trace carry before the board heats too much? It uses the IPC-2221 relationship between cross-sectional area, temperature rise and current. **Sections:** #### How to use it **Body:** Enter the finished trace width and pick the copper weight from the stackup. Choose external or internal layer, then set the temperature rise you can tolerate above ambient. The maximum current appears instantly, and the chart shows how current capacity grows as the trace gets wider. Use the density output as a sanity check, because very high amps per square mm usually mean you should widen the trace or add copper pour. #### The formula behind it **Body:** IPC-2221 gives I = k x dT^0.44 x A^0.725, where I is current in amps, dT is temperature rise in degrees C, and A is the cross-sectional area in square mil. The constant k is 0.048 for outer layers and 0.024 for inner layers. Area is width in mil times thickness in mil, and 1 oz copper is about 1.378 mil thick. **Bullets:** - Capacity is not linear in width: doubling area adds about 65% current - Temperature rise has a weak 0.44 exponent - Inner layers carry roughly half the current of outer layers #### Reading the result **Body:** Worked example: a 1 mm trace in 1 oz copper on an outer layer with a 20 C rise carries about 3.2 A. Pick a rise that suits the product, since a 10 C rise is conservative for medical or aerospace boards, while consumer power boards often accept 30 C or more. Remember the board still has to survive reflow, rework and the maximum ambient of the end product. #### Common mistakes **Body:** Using the wrong copper thickness after plating is common: outer layers start from a base foil that gains plating, so finished copper is heavier than the foil callout. Another mistake is ignoring neck-downs at pads and vias, which become the hottest points. Always check the narrowest section of a power path, not the typical width. **Cta:** If your PCBA drawings and BOM data live in an ERP, Netray can help route design rules and approvals into the engineering change flow. **Faq:** #### Is IPC-2221 still the right reference? **Answer:** IPC-2221 trace curves date from older testing. IPC-2152 is the newer current-carrying standard and accounts for board thickness and planes. IPC-2221 remains a common quick estimate and is usually conservative. #### What temperature rise should I choose? **Answer:** Many designers use 10 C to 20 C for reliable products and up to 30 C for cost-driven boards. Choose based on the maximum ambient, the laminate Tg and the lifetime requirement of your product. #### Why are inner layers rated lower? **Answer:** Inner traces are surrounded by dielectric, which conducts heat worse than air convection and radiation from the surface. The IPC-2221 constant for inner layers is half that for outer layers. #### Does this cover vias? **Answer:** No. Vias have their own current limits based on barrel plating thickness and diameter. Use several vias in parallel for power paths and verify the plating thickness with your fabricator. ## Search terms pcb trace current capacity calculator, trace current temperature rise, ipc-2221 current calculator, how much current can a pcb trace carry, pcb trace ampacity, copper weight trace current, internal vs external trace current, pcb current density calculator --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json