PCB Trace Width Calculator
IPC-2221 Standard — Internal & External Layers
The most accurate free PCB trace width calculator online. Based on the IPC-2221 standard, calculate the minimum copper trace width needed to safely carry your target current — for both external and internal PCB layers — including trace resistance, voltage drop, and power loss.
What is PCB Trace Width?
The Critical Dimension in Every PCB Layout
PCB trace width is the physical width of a copper conductor routed on a printed circuit board. It is one of the most critical parameters in PCB layout design — directly determining how much current a trace can safely carry without overheating. An undersized trace causes resistive heating, voltage drop, and eventual board failure. An oversized trace wastes board space and increases manufacturing cost. The PCB trace width calculator below computes the exact minimum width needed for your current, copper thickness, and permissible temperature rise — following the industry-standard IPC-2221 guidelines.
⚡ Current Carrying Capacity
Every PCB trace has a maximum current it can safely conduct. Exceeding the PCB trace current carrying capacity causes resistive heating proportional to I²R — which can melt solder, delaminate the board, or cause open-circuit failure.
🌡 Temperature Rise
The PCB trace temperature rise above ambient is directly controlled by trace width and copper thickness. IPC-2221 recommends a maximum ΔT of 10°C for signal traces and up to 20–30°C for power traces in most applications.
📐 IPC-2221 Standard
The IPC-2221 standard defines empirical formulas for minimum trace width based on cross-sectional area, using different k-factors for external (0.048) and internal (0.024) copper layers to account for heat dissipation differences.
Free Online PCB Tool
PCB Trace Width Calculator — IPC-2221
Enter your current, copper thickness, temperature rise, and trace length below. Our free PCB trace width calculator instantly returns the minimum trace width, resistance, voltage drop, and power loss for both external and internal copper layers — following the IPC-2221 standard used by professional PCB designers worldwide.
PCB Trace Width Calculator (IPC-2221)
Find the minimum trace width for a given current and temperature rise on internal and external layers — plus resistance, voltage drop and power loss.
Formula & assumptions
I = k × ΔT0.44 × A0.725 → A = (I ÷ (k × ΔT0.44))1/0.725
Width = A ÷ (thickness × 1.378) — A in mil², thickness in oz/ft² (1 oz = 1.378 mil = 35 µm). k = 0.048 for external layers, 0.024 for internal layers.
Resistance uses copper resistivity 1.72 × 10⁻⁸ Ω·m at 20 °C with a temperature coefficient of 0.00393 /°C, evaluated at ambient + temperature rise.
IPC-2221 curves are valid up to 35 A (external) / 17.5 A (internal), 10–100 °C rise, widths up to 400 mil and 0.5–3 oz copper. For high-current or thermally critical boards, check against IPC-2152, which also accounts for board material, planes and thickness.
IPC-2221 Formula
How to Calculate Trace Width of a PCB — The Formula
The IPC-2221 standard uses empirical formulas derived from test data to determine the minimum PCB trace width needed for a given current and temperature rise. Our PCB trace width calculator implements these formulas exactly.
Calculate Cross-Sectional Area
[ I ÷ (k × ΔT 0.44) ] 1/0.725
Where I = current (A), k = layer constant, ΔT = permissible temperature rise above ambient (°C). This gives the minimum copper cross-section needed in square mils.
Calculate Minimum Trace Width
Area ÷ (Thickness × 1.378)
Copper thickness in oz/ft² is converted to mils (1 oz ≈ 1.37 mil). Dividing area by the effective thickness gives the minimum trace width. Convert to mm by multiplying by 0.0254.
Calculate Trace Resistance
ρ_T = ρ₂₀ × [1 + 0.00393 × (T − 20)]
ρ₂₀ = 1.72×10⁻⁸ Ω·m for copper at 20°C. Temperature correction factor α = 0.00393/°C. L = trace length, A = cross-sectional area in m².
Calculate Voltage Drop & Power Loss
P_loss (W) = V_drop × I = I² × R
Voltage drop across the trace is Ohm's Law applied to trace resistance. Power loss (heat dissipated) equals I²R — this is the resistive heating that drives the temperature rise in the trace.
The key difference between external and internal PCB trace current calculator results is the k-factor. External layers dissipate heat to ambient air; internal layers are insulated by FR4 dielectric and run hotter at the same current.
Use this table as a quick guide for common PCB trace width current requirements. Always verify with the calculator above for your specific copper thickness and temperature conditions.
| Current (A) | Min. Width (mil) Ext. | Min. Width (mm) Ext. | Min. Width (mil) Int. | Min. Width (mm) Int. | Typical Use |
|---|---|---|---|---|---|
| 0.3 A | 4.0 | 0.10 | 9.0 | 0.23 | Signal / GPIO |
| 0.5 A | 7.5 | 0.19 | 16.5 | 0.42 | Low-power signal |
| 1.0 A | 17.4 | 0.44 | 38.4 | 0.98 | Power supply rail |
| 2.0 A | 38.0 | 0.97 | 83.7 | 2.13 | Motor driver |
| 3.0 A | 62.4 | 1.58 | 137.6 | 3.49 | High-current power |
| 5.0 A | 116.2 | 2.95 | 256.4 | 6.51 | Power converter |
| 10.0 A | 261.3 | 6.64 | 576.6 | 14.6 | High-power / bus bar |
Step-by-Step Guide
How to Calculate PCB Trace Width — 5 Steps
Follow these steps to determine the correct copper trace width for your PCB design using the IPC-2221 PCB trace width calculator above or manually using the formula.
-
1
Determine the Required Current
Identify the maximum continuous current the PCB trace must carry. For power supply traces, use the worst-case load current. For signal traces carrying transient currents, use the RMS value. Always add a 20–25% safety margin above the nominal operating current.
💡 Example: If your load draws 2A, design for at least 2.4A (20% margin). -
2
Select Copper Thickness and Layer
Standard PCBs use 1 oz/ft² copper (≈35µm / 1.37 mil). Heavy copper boards use 2 oz (2.74 mil) or higher. Determine whether your trace is on an external (outer) or internal (inner) layer — internal layers require wider traces for the same current due to reduced heat dissipation through FR4.
💡 1 oz copper = 1.37 mil = 0.035mm thickness. -
3
Set Permissible Temperature Rise
The PCB trace temperature rise (ΔT) is the acceptable increase in trace temperature above ambient. IPC-2221 recommends ΔT = 10°C for general signal traces and up to 20–30°C for dedicated power traces. Lower ΔT values give more conservative (wider) trace widths.
💡 Use ΔT=10°C for signal traces, ΔT=20°C for power rails. -
4
Calculate Using the PCB Trace Width Calculator
Enter your current, copper thickness, temperature rise, ambient temperature, and trace length into the PCB trace width current calculator above. Click Calculate to instantly get the minimum trace width in both mil and mm, plus trace resistance, voltage drop, and power loss for both external and internal layers.
💡 Use the result from the external layer for top/bottom copper, internal layer for mid-stack layers. -
5
Apply in PCB Layout and Verify
Set your trace width constraint in your EDA tool (Altium Designer, Cadence Allegro, KiCad) to the calculated minimum. For high-current traces, round up to the next standard width. Verify that the voltage drop does not exceed 5% of the supply voltage and that power loss is within thermal limits of your PCB stack-up.
💡 For complex multi-layer PCB design with impedance control, see our PCB Layout Design services.
Why Use a Calculator
Benefits of Using a PCB Trace Width Calculator
Prevent Trace Burnout
An undersized trace acts as a fuse — it heats up under load and can melt solder joints, delaminate FR4, or cause open-circuit failure. The calculator ensures your PCB trace current carrying capacity is never exceeded.
IPC-2221 Compliance
Designs validated against IPC-2221 pass manufacturer DFM checks and meet industry quality standards. Compliance is mandatory for aerospace, medical, and industrial PCB designs.
Minimise Voltage Drop
The PCB trace resistance calculator output lets you verify that voltage drop across long power traces does not cause logic-level or regulation issues in sensitive circuits.
Thermal Management
Knowing power loss (I²R) per trace helps plan copper pours, thermal vias, and heatsinking for high-power boards — preventing hot spots that reduce component lifetime.
Optimise Board Space
Oversized traces waste precious PCB real estate, especially in high-density designs. Using the exact minimum width from a trace width calculator for PCB maximises routing density.
Internal vs External
Automatically calculates both internal and external layer requirements. Internal traces in multi-layer PCBs need significantly wider copper due to the insulating effect of FR4 dielectric on heat dissipation.
Professional guidelines for reliable PCB trace width and spacing design in production boards.
- ✓Always add a 20–25% safety margin above the IPC-2221 minimum calculated trace width.
- ✓Use ΔT = 10°C for signal traces; up to 30°C for dedicated power traces only.
- ✓For traces >5A, use copper pours (filled polygons) rather than routed traces.
- ✓Keep voltage drop below 5% of supply voltage on any power distribution trace.
- ✓Internal layers need ~2× the trace width of external layers for the same current.
- ✓Use thermal vias under high-power components to improve trace current capacity.
- ✓Verify IPC-2152 (newer empirical data) for safety-critical or automotive designs.
- ✓Minimum manufacturable trace width is typically 0.1mm (4 mil) for standard PCB fabs.
Need Expert PCB Layout Design with Correct Trace Sizing?
Our senior PCB engineers use industry-leading EDA tools — Altium Designer and Cadence Allegro — to design production-ready boards with precise trace width calculation, impedance control, and full IPC-2221 compliance from schematic to Gerber.
Explore PCB Layout Design →FAQ
Frequently Asked Questions — PCB Trace Width Calculator
Clear, direct answers to the most common questions about PCB trace width calculation, IPC-2221, current capacity, and trace sizing best practices.
To calculate trace width of a PCB, use the IPC-2221 empirical formula. First, calculate the required copper cross-sectional area using: Area (mil²) = [I ÷ (k × ΔT^0.44)]^(1/0.725) where I is current in Amperes, k is the layer constant (0.048 for external, 0.024 for internal layers), and ΔT is the permissible temperature rise in °C above ambient.
Then convert area to trace width: Width (mil) = Area ÷ (Thickness × 1.378) where thickness is in mils (1 oz copper = 1.37 mil). Convert the result to mm by multiplying by 0.0254. For example, a 1A trace on an external layer with 1 oz copper and ΔT=10°C requires a minimum width of approximately 17.4 mil (0.44mm). Use our free PCB trace width calculator above to solve this instantly for any input values.
A good PCB trace width depends on the current the trace must carry. For standard 1 oz copper with a 10°C temperature rise, use these guidelines for external layers: signal traces carrying under 0.3A can be as narrow as 0.1mm (4 mil — the manufacturing minimum). Traces carrying 1A need at least 0.44mm (17.4 mil). Power traces carrying 3A need at least 1.58mm (62 mil). For 5A, plan for at least 2.95mm (116 mil).
In general, a good trace width for a PCB is the IPC-2221 calculated minimum plus a 20% safety margin. Never use the theoretical minimum without margin — manufacturing tolerances, temperature variation, and current spikes can all reduce safety headroom. For signal traces with no current concern, 0.15–0.2mm (6–8 mil) is a practical standard in most PCB fabs. For high-speed signals, trace width also affects characteristic impedance — use an impedance-controlled PCB layout for those cases.
PCB trace current carrying capacity is the maximum continuous current a copper trace can conduct without the resulting I²R resistive heating causing the trace temperature to rise beyond a safe limit. It is determined by the trace width, copper thickness, layer position (external vs internal), and the ambient operating temperature of the board.
For standard 1 oz copper (35µm), 0.2mm traces can typically carry around 0.5A (external), while 1mm traces can carry approximately 2.5A. Internal layers have approximately 50% of the current capacity of external layers of the same width because FR4 dielectric is a thermal insulator and prevents heat dissipation. Exceeding the current capacity causes resistive heating, solder joint degradation, board delamination, and eventually trace burnout — an open circuit failure.
The IPC-2221 trace width formula is an empirical equation derived from thermal test data on copper conductors on PCBs. It has two steps: First calculate the minimum cross-sectional area in square mils: Area = [I ÷ (k × ΔT^b)]^(1/c). Then calculate minimum width: Width (mil) = Area ÷ (t × 1.378).
Constants: b=0.44, c=0.725 for both layer types. k=0.048 for external layers, k=0.024 for internal layers. t = copper thickness in oz/ft². The factor 1.378 converts oz/ft² thickness to mils per unit area. This formula is implemented exactly in the PCB trace width current calculator above. Note that IPC-2152 (2009) provides updated empirical data that some engineers prefer for more conservative results.
PCB trace resistance is the DC electrical resistance of a copper conductor on a printed circuit board. It is calculated using: R = ρ × L ÷ A where ρ is copper resistivity (1.72×10⁻⁸ Ω·m at 20°C), L is trace length in metres, and A is cross-sectional area in m² (width × thickness).
Resistivity increases with temperature: ρ_T = ρ₂₀ × [1 + 0.00393 × (T − 20)]. At 50°C ambient, copper resistivity is about 12% higher than at 20°C. The PCB trace resistance calculator built into this tool automatically applies temperature correction based on your ambient temperature input. Higher resistance causes more voltage drop (V=IR) and more power loss (P=I²R), both of which increase trace temperature — creating a thermal feedback loop that must be managed through correct trace sizing.
PCB trace temperature rise (ΔT) has a direct inverse relationship with the required trace width. A higher allowed temperature rise means you can use a narrower trace for the same current — because a narrower trace is allowed to run hotter. Conversely, a lower ΔT limit demands a wider trace to keep the same current within thermal bounds.
For example, a 2A trace on an external layer with 1 oz copper requires 38 mil (0.97mm) at ΔT=10°C, but only 21 mil (0.54mm) at ΔT=30°C. While using a higher ΔT allowance saves board space, it reduces component reliability — every 10°C increase in operating temperature roughly halves the lifetime of nearby electrolytic capacitors and semiconductor junctions. IPC-2221 recommends a maximum ambient + ΔT of 105°C for most commercial PCB materials (FR4 Tg 130°C rated boards).
