Voltage Drop Calculator (NEC 3% & 5% Standards)
Calculate voltage drop across AC/DC single-phase circuits based on wire gauge, conductor material, and distance.
Enter Your Dimensions
US • ftHow We Calculated This
• Motors and compressors operating below 90% rated voltage draw higher current and may overheat prematurely.
Formula & Volumetric Method
Voltage Drop Vd = (2 × K × I × L) ÷ Circular Mils. Copper K ≈ 12.9 Ω·cmil/ft, Aluminum K ≈ 21.2 Ω·cmil/ft.
Calculations are performed strictly using standard civil engineering constants. Volumetric outputs are normalized to true compaction rates, ensuring purchased quantities match jobsite yields.
Jobsite Engineering Guidelines
- NEC recommends maximum 3% voltage drop on branch circuits for optimal equipment efficiency.
- Total voltage drop from service panel to furthest outlet should not exceed 5%.
- Upsizing wire by one gauge (e.g., #12 AWG to #10 AWG) resolves excessive voltage loss on long runs.
Frequently Asked Questions
How accurate is the Voltage Drop Calculator (NEC 3% & 5% Standards) for ordering materials?
Our calculations match standard store packaging sizes in the US, Canada, UK, and Australia. We include a safety waste buffer (default 8% to 12%) so you do not run short due to uneven ground or spillage.
Why should I add extra for waste when ordering?
Uneven ground, cutting scrap, and leftover mix in the wheelbarrow or mixer drum consume an extra 5% to 15% of material. Ordering only the exact measurement usually leaves you short, which can lead to expensive extra delivery fees.
Does this calculator support both Imperial and Metric units?
Yes. You can switch between US Customary (feet, inches, cubic yards, pounds), Canadian units, UK metric, and Australian standards using the region selector in the header or the unit dropdown on each input.