Convert American Wire Gauge (AWG) to diameter, area, and resistance. Calculate voltage drop, power loss, and a simplified ampacity reference for educational understanding. ⚠️ For actual electrical installations, consult licensed electricians and local NEC codes—this calculator is a learning tool only.
Last Updated: 5/6/2026
Range: 0–14 AWG (or −3 to +4 for larger gauges). Lower AWG = thicker wire.
One-way distance (typical: 50–200 ft)
Circuit current or load
Standard: 120V (single-phase residential), 240V (split-phase, dryer/range)
American Wire Gauge (AWG), officially known as Brown & Sharpe gauge, is the standardized system for specifying the cross-sectional area (and hence diameter and resistance) of round, solid, nonferrous electrical conductors used in North America. The system employs a logarithmic scale: as AWG number decreases by 6, the wire diameter doubles, and the cross-sectional area (and current-carrying capacity) quadruples. For example, 10 AWG has twice the diameter of 16 AWG. This geometric progression means AWG provides an intuitive numerical system for electrical engineers: starting from 14 AWG (typical residential lighting circuits, ~15 A capacity), each step down (13, 12, 11, etc.) represents progressively thicker, higher-capacity wire. Conversely, AWG 18–28 is used for low-power applications (signals, data, bell wire). The relationship is: diameter d (mm) = 0.127 × 92^((36−n)/39), where n is the AWG number. A 12 AWG wire (common household general-purpose circuit) has ~2.05 mm diameter, 5.2 mm² cross-section, and ~1.6 Ω per kilometer (at 20°C copper). Understanding wire gauge is essential for electrical safety: undersized wires overheat, causing fire hazards; oversized wires waste material and cost. The National Electrical Code (NEC) specifies ampacity (maximum continuous current) tables based on wire gauge, insulation type (60°C, 75°C, or 90°C), and installation conditions. A 12 AWG copper wire with 60°C insulation (common thermostat/THHN wire) has 20 A ampacity; the same gauge at 90°C insulation permits 25 A. These limits account for I²R heating in the conductor: at 20 A through 12 AWG (~0.16 Ω/100 ft), power dissipation is ~0.64 W per 100 feet, raising conductor temperature by ~50°C above ambient in free air. Exceeding ampacity causes insulation degradation and fire risk. Equally critical is voltage drop, calculated via Ohm's law: V_drop = I × R × L, where L is loop length (out and back, hence ×2 for DC or low-frequency single-phase AC). The NEC mandates branch-circuit voltage drop ≤ 3% of supply voltage (e.g., ≤3.6 V on 120 V); exceeding this causes light dimming, motor sluggishness, and power loss. For example, a 100 A subpanel fed 200 feet from main service via 4 AWG copper (~0.01 Ω/100 ft) incurs V_drop ≈ 100 A × 0.02 Ω × 2 = 4 V (3.3% of 120 V, acceptable; 4 V of 240 V is 1.7%, excellent). The calculator above integrates these critical parameters: it computes diameter and area (basic wire properties), resistance per kilometer (material and temperature dependent), ampacity (NEC-based, accounting for wire gauge and material), voltage drop (for given current and length), and power loss (thermal implications). For practical circuit design, this tool enables rapid "what-if" analysis: "If I run a 15 A kitchen outlet 80 feet from the panel using 12 AWG copper, will voltage drop stay within 3%?" (Answer: 15 A × 0.32 Ω × 2 ÷ 120 V ≈ 0.8%, acceptable). Alternatively: "What gauge do I need for 50 A over 150 feet to stay under 3% drop?" (Working backward, max drop 3.6 V at 120 V, need R_total ≤ 0.048 Ω, or 0.024 Ω per 150 feet; requires 3 AWG or better).
Material selection (copper vs. aluminum) impacts both resistance and cost. Copper has ~58% lower resistivity than aluminum (~1.68 × 10⁻⁸ Ω·m vs. 2.75 × 10⁻⁸ Ω·m), making copper the superior conductor electrically but also more expensive (~8–10× material cost). Transmission lines use aluminum for cost; distribution circuits and household wiring favor copper for its lower resistance (reducing losses) and superior corrosion resistance (aluminum oxidizes faster, creating intermittent contact issues at splices). Aluminum wiring, popular in the 1970s–80s due to copper scarcity, now carries a reputation for safety issues—aluminum has higher thermal expansion and softens at lower temperatures than copper, leading to loose connections and fire hazards in older installations. Modern aluminum wire is rarely used in homes; when it is, oversizing (e.g., using 10 AWG aluminum instead of 12 AWG copper for the same application) is mandated. Stranded vs. solid conductors affect practical use: solid wire (single rod) is rigid, suitable for fixed-installation like in-wall circuits; stranded wire (multiple thin filaments bundled) is flexible, ideal for appliance cords and machine tools. At high frequencies (radiofrequency engineering), skin effect becomes relevant: current flows preferentially on the wire's surface, effectively increasing resistance; this drives the use of hollow copper tubes or silver-plated surfaces for microwave transmission lines. The calculator assumes DC or low-frequency (≤60 Hz) AC, where skin effect is negligible; for RF applications (MHz and above), specialized impedance and attenuation calculations are required. Practical installation factors: bundled cables in conduit trap heat, reducing ampacity by ~50% or more (derated in NEC tables); outdoor exposure or burial requires UF (underground feeder) or USE (underground service entrance) rated insulation; high-temperature environments (furnace rooms, attics) require 90°C insulation to maintain capacity. This tool provides the foundational circuit analysis; real-world wiring decisions also involve raceway sizing, conduit fill, termination hardware (lugs, connectors), and compliance with local electrical codes.
Enter the AWG number for the wire you're analyzing or selecting. Common residential gauges: 14 AWG (lighting, 15 A), 12 AWG (general purpose, 20 A), 10 AWG (heavy appliances, 30 A), 8 AWG (range/dryer, 40–50 A). Industrial: 4 AWG (70 A), 2 AWG (95 A), 1 AWG (110 A), 0/1/0 AWG (125–200 A). Larger gauges extend to −4 (230 A) and beyond for utility distribution. Smaller gauges (16–28 AWG) are used for signal wiring, data cables, and bell circuits.
Wire length is the one-way distance from power source to load (e.g., from circuit breaker panel to wall outlet). The calculator internally doubles this for the voltage drop calculation (current flows out and back). Example: breaker panel to kitchen outlet = 80 feet one-way; calculator uses 160 feet for loop. Circuit current is the expected continuous load through the wire (e.g., 15 A circuit, 20 A circuit); for motors, multiply nameplate amps by 1.25 per NEC. For sizing unfamiliar circuits, use typical loads: 15 A (lighting, outlets), 20 A (kitchen countertop), 30 A (range, dryer—typically cooktop branch), 50 A (large electric range, subpanel feeder).
Copper: lower resistance, higher ampacity, preferred for household and industrial use; more expensive. Aluminum: higher resistance (~1.6× for same AWG), lower ampacity (~0.85× that of copper), lower cost; used for transmission lines and occasionally in commercial wiring but rarely in homes due to safety/reliability concerns. Aluminum requires oversizing and special precautions at terminations. For residential applications, always specify copper unless budget constraints dictate otherwise.
Key outputs: (1) Diameter and cross-sectional area (fundamental wire properties, for reference). (2) Ampacity (simplified reference only)—this is a base-case estimate for common residential gauges; actual safe ampacity depends on insulation rating (60°C, 75°C, 90°C), bundling, temperature, and installation. Consult NEC Article 310 for your specific situation. (3) Voltage drop (voltage lost in the wire at the specified current; <3% is a common guideline for branch circuits). (4) Power loss (watts dissipated as heat; high losses indicate inefficiency and heating). (5) Category (classification: "General Purpose," "Heavy Duty," etc., for context). Color-coded warnings alert if estimated ampacity is exceeded (red) or voltage drop > 3% (orange). Green checkmark indicates acceptable for reference purposes.
⚠️ This calculator is an educational tool, not a substitute for licensed electrician expertise or NEC compliance. Use iteratively to understand wire sizing: start with estimated AWG, check if the simplified ampacity reference and voltage drop seem reasonable for your load. Example workflow: Planning a 20 A circuit 120 feet from breaker to bathroom. Try 14 AWG: estimated ampacity 15 A (marginal for 20 A ✗). Try 12 AWG: estimated ampacity 20 A (✓), voltage drop ~1.2% (✓). For actual installation, verify with NEC tables (Article 310 for your insulation rating), derating factors, and local codes. Always consult a licensed electrician for real circuits.
Scenario: Homeowner is adding a dedicated 20 A countertop outlet to the kitchen, 90 feet from the main electrical panel. Select the appropriate wire gauge (copper) ensuring both ampacity accommodates peak loads and voltage drop doesn't exceed 3% (NEC requirement). Calculate voltage drop and power loss at full 20 A load.
Counterintuitive but historical: AWG numbering descends as wire thickens. The system originated from draw gauge scales in wire manufacturing; smaller numbers indicated fewer drawing operations (less reduction = thicker wire). By convention, this reverse numbering persisted. As a mnemonic: think 'gauge' as a reduction tool—higher reduction (higher AWG) = thinner wire. Practical: memorize a few references (12 AWG ≈ 2 mm diameter, and every 6-AWG decrease doubles diameter). Modern metric systems (IEC) use wire cross-section in mm² directly, avoiding confusion, but AWG is entrenched in North American electrical practice.
Ampacity (maximum continuous current wire can handle safely) should align with circuit breaker trip rating; breaker protects the wire. Example: 12 AWG copper has a simplified ampacity reference of ~20 A in this calculator, so a 20 A breaker is typical (not 30 A). HOWEVER: Real ampacity depends on insulation rating, bundling, temperature, and installation—consult NEC Article 310 for your exact situation. The principle: breaker rating should not exceed wire ampacity. If you placed a 30 A breaker on 12 AWG wire, the breaker wouldn't trip until 30 A, but the wire might overheat before that, causing fire. Conversely, undersized breakers are safe but inconvenient. For motors and other inductive loads, NEC requires breaker >= 1.25× motor nameplate amps, adding complexity. Always verify with NEC tables and a licensed electrician for real installations.
Resistance increases with temperature (~0.4% per °C for copper above 20°C). A 12 AWG wire at 0°C has lower resistance than the same wire at 50°C. FOR AMPACITY: Higher temperatures significantly reduce the safe limit. NEC tables specify ampacity at different insulation temperature ratings: 60°C, 75°C, or 90°C. A 12 AWG THHN wire (90°C insulation) is rated higher than the same wire with 60°C insulation. IMPORTANT: This calculator uses simplified 60°C reference values and doesn't account for ambient temperature. In hot environments (attics, furnace rooms), ampacity must be derated by 10–50% per NEC tables, or use 90°C-rated insulation. The calculator assumes 20°C ambient; for hot environments, multiply resistance by 1.004 per °C above 20°C, yielding higher voltage drops. Consult NEC Article 310 for your specific installation.
Solid wire: single rod, rigid, cheaper, used for fixed buried or in-wall circuits (branch wiring). Stranded wire: multiple thin filaments bundled, flexible, used for appliance cords, flexible conduit connections, and high-motion applications. Electrically, both solid and stranded of the same AWG have similar resistance and ampacity (assuming the stranded wire's cross-section matches). Practically, stranded is easier to connect (bends at terminals), while solid is stiffer (harder to install but resists accidental damage). In-wall NEC code typically requires solid Romex (NM cable) or stranded in conduit; appliances use stranded cords. The calculator treats both the same; if you know your wire is stranded, ensure the AWG refers to the overall conductor cross-section, not individual strand diameter.
Counterintuitive: we'd expect very large wire to minimize resistance. In fact, power transmission lines use massive conductors not primarily for resistance reduction but for current-carrying capacity and cost optimization. At, say, 500 kV, a smaller conductor would cause excessive power loss (P_loss = I² × R; high current × resistance = huge waste). But at higher voltage, the same power (P = V × I) requires proportionally less current, reducing losses. Example: 1 MW at 12 kV requires 83 A; at 500 kV, only 2 A. The 2 A through thin wire has negligible loss; the 83 A through thin wire would have catastrophic loss. Thus, transmission uses ultra-high voltage (345–765 kV) with moderate copper wire (size determined by voltage stress and mechanical load, not ampacity). Distribution lines to homes use much lower voltage (7–35 kV) and larger conductors, and finally, household circuits at 120/240 V use further larger conductors relative to power transmitted. This hierarchical optimization (voltage up, current down, conductor size adjusted accordingly) is the art of electrical system design.
NEC = National Electrical Code, established by NFPA (National Fire Protection Association), sets minimum safety standards for electrical installations in the USA (other countries have equivalents: Canadian Electrical Code, IEC in Europe). NEC specifies wire ampacity, breaker coordination, grounding, conduit sizing—basically all electrical safety. Local jurisdictions adopt NEC (sometimes with amendments) and enforce it via electrical inspections. You must follow NEC (or adopted local code) because: (1) it's the law; (2) failure voids homeowner's insurance; (3) unsafe installations cause fires, electrocution, equipment damage. Electrical contractors are licensed because they've demonstrated NEC knowledge. The calculator applies NEC ampacity tables (60°C insulation baseline); for other conditions (high temperature, bundled cables, etc.), consult NEC Article 310 derating factors.
Feeder sizing is more complex than branch circuits: voltage drop over long runs is significant, and ampacity depends on distance and load. For a 100 A feeder 100 feet (50 feet one-way) at 120/240 V, trying 4 AWG copper: resistance ≈ 0.005 Ω/100 ft, round-trip ≈ 0.01 Ω, V_drop = 100 A × 0.01 Ω = 1 V (0.42% of 240 V, acceptable). Ampacity of 4 AWG = 70 A, too low for 100 A feeder. Need 2 AWG (ampacity 95 A, still marginal) or 1 AWG (ampacity 110 A, better). 1 AWG copper, 100 feet: V_drop ≈ 0.5 V (~0.2% of 240 V, excellent), power loss ~5 kW (acceptable for feeder). Feeder design requires balancing voltage drop, ampacity, and cost; the NEC permits up to 3% combined feeder + branch circuit drop. For large feeders, consider aluminum (85% of copper resistance, lower cost but larger gauge needed), or run separate larger feeds if distance/load justify.
CRITICAL GAP IN THIS CALCULATOR: Real ampacity requires applying NEC derating factors. NEC Table 310.15(B)(2) specifies 'Ampacity of Multiple Current-Carrying Conductors' (bundling derating): when 4+ conductors are in conduit/cable, heat dissipation drops, so ampacity is reduced. Example: 4–6 conductors → × 0.80, meaning a wire normally rated 20 A carries only 16 A. Similarly, ambient temperature above 30°C reduces ampacity per NEC Table 310.15(B)(1): 40°C ambient with 90°C insulation → × 0.82 factor. High altitude also applies. IMPORTANT: This calculator assumes residential Romex (2–3 conductors, minimal derating, ambient 20–30°C) and shows base 60°C ampacity—NOT site-specific or real-world ampacity. Industrial/commercial installations with bundling, high temperature, or altitude require significant derating (20–50% reduction). Always consult NEC Article 310 Tables and derating sections, plus a licensed electrician, before sizing wire for actual work.
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