Electrical calculators
Wire Size / Ampacity Calculator
Estimate a minimum conductor size from load current, continuous-load planning, material, cable type, ambient temperature, and current-carrying conductors.
Ampacity screen
A
Temp + count
AWG
Ampacity is only one sizing check. Voltage drop, overcurrent protection, terminations, wiring method, and local code still control the final installation.
Input Dimensions
Calculation Results
Planning estimate only
Results are based on the values and assumptions entered here. Confirm quantities with current product information and suppliers; use qualified local professionals for structural, safety-critical, permitted, or code-regulated work.
Read the calculator terms and limits →How to Use the Wire Size Calculator
Enter the load current and choose whether it is a continuous load for this preliminary screen. Then select copper or aluminum, the cable type, the termination temperature rating, ambient temperature, and the number of current-carrying conductors. The calculator applies a simplified ampacity table and returns the first conductor in its supported range that meets the planning design current.
The calculator is intentionally conservative about what it claims. It does not select a breaker, approve a wiring method, calculate conduit fill, or complete a voltage-drop design. Use the separate Voltage Drop Calculator when run length and load voltage are part of the design review.
How Ampacity Is Screened
Base ampacity depends on conductor size, metal, and temperature rating. Ambient temperature correction can reduce the allowable value, and additional current-carrying conductors can require an adjustment factor. The final planning value is limited by the selected termination rating and, for NM-B or UF-B, the cable’s 60°C limitation in this simplified model.
The workflow follows the structure of NEC ampacity tables: start with the conductor table, apply the relevant correction and adjustment factors, then observe the equipment termination limit. Actual installations require the correct edition of the applicable code, product listing, wiring method, equipment rating, and local amendments.
Safety and Limitations
This page is an educational planning tool, not an electrical design approval. Incorrect conductor sizing can cause overheating, fire, shock, equipment damage, or death. Do not use the suggested size as the final answer for a permitted, inspected, service, motor, dwelling, solar, EV, or other safety-critical installation without review by a qualified electrical professional.
Before ordering or installing, verify ampacity, overcurrent protection, voltage drop, termination ratings, conductor insulation, ambient conditions, bundling, raceway or cable listing, grounding, and local code requirements. Product data and the authority having jurisdiction control when they differ from this estimate.
Frequently Asked Questions
What does this wire size calculator calculate?
It provides a preliminary minimum conductor size from a simplified ampacity table, load current, continuous-load factor, conductor material, cable type, ambient temperature, and current-carrying conductors.
Does the calculator choose the final wire size?
No. Final sizing also depends on the applicable code, overcurrent protection, termination limits, installation method, voltage drop, raceway or cable listing, equipment instructions, and local inspection requirements.
Why do temperature and conductor count matter?
Higher ambient temperature can reduce allowable ampacity, while more current-carrying conductors can require an adjustment factor. Both can make a larger conductor necessary.
Should I use this result for a permitted installation?
Use it only as a planning screen. Have the final conductor, breaker, wiring method, and installation reviewed by a qualified electrical professional under the applicable local code.
Reference context: NFPA publishes the NEC ampacity workflow and tables; Schneider Electric reproduces the NEC ampacity table context and termination notes; manufacturer guidance remains necessary for the selected product and installation.