DC Wire Size Calculator
This DC wire size calculator finds the minimum AWG wire gauge for your direct-current circuit. It checks two independent limits — the wire must carry the current safely (ampacity) and waste no more than your allowed voltage drop. People arrive here searching for a dc wire size calculator solar installers trust, an rv wire size calculator, an automotive wire gauge calculator, or a dc voltage drop calculator — one tool covers all of them, because the underlying physics is identical. For 12V-only projects you may also like our dedicated 12V wire size calculator.
Compare nearby sizes
| AWG | mm² | Drop | Drop % | Ampacity | Verdict |
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How DC Wire Sizing Works
A DC wire size calculation answers two separate questions. First: can the wire carry the current without overheating? That is the ampacity limit, set by the wire's cross-section and insulation. Second: how much voltage is lost along the run? That is the voltage-drop limit. The correct wire size is the smallest gauge that passes both tests — a wire that is safe but drops 8% of a 12V battery's voltage will still make your equipment misbehave.
The DC voltage-drop formula
Where I is current in amps, R is the wire's resistance per meter (which rises with temperature), and L is the one-way length. The factor of 2 accounts for the round trip: current flows out on the positive wire and back on the negative wire, so both conductors drop voltage. This is why this calculator asks for the one-way length and doubles it internally — a common mistake in DC cable sizing is forgetting the return run. In short, this page doubles as a dc voltage drop calculator: every result shows the exact volts and percent lost, plus a comparison table for the gauges around it.
The 3% rule (and when 10% is fine)
Marine standard ABYC E-11 — widely adopted for RV and off-grid DC work — allows 3% drop for critical circuits (navigation, charging, inverters, anything where low voltage causes faults) and 10% for non-critical circuits (cabin lights, fans). Automotive practice is similar: keep starter, ECU and audio power feeds at 3% or better. This calculator defaults to 3%.
Continuous loads get a 125% margin
Solar arrays, inverters and chargers run for hours. Electrical codes treat such continuous loads at 125% of their rated current, and this calculator does the same when "Continuous duty" is checked: a 40 A continuous load is sized as if it were 50 A. Uncheck it only for genuinely intermittent loads (horns, winches, door locks).
DC Ampacity Chart (Copper, Conservative)
Maximum current per AWG size used by this dc wire size calculator. These are conservative single-conductor DC ratings; aluminum ampacity is derated to 78% of these values. "Continuous" is the wire's limit for a continuous load after the 125% sizing margin is applied. Use this chart as a battery cable size calculator for starter, house-bank and inverter feeds, or for any low voltage wire size question from 12 V to 48 V and beyond.
| AWG | mm² | Ω / km @20°C | Max amps | Continuous load ≤ |
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Bundle many wires in a conduit, run them through a hot engine bay, or use thinner insulation, and real ampacity drops further — derate or go one size up. When in doubt, the thicker wire is always the safer choice.
Worked Examples
Example 1 — Solar: 400 W array at 24 V, 12 m one-way
Current = 400 ÷ 24 = 16.7 A. At 3% max drop and 75°C copper: 8 AWG drops 4.18% (fails), 6 AWG drops 2.61% (passes) with 75 A ampacity — comfortably above the 20.8 A continuous-duty requirement. Answer: 6 AWG copper. This is the classic off-grid solar wire size problem: long roof-to-controller runs force surprisingly thick wire at 24 V, which is one reason many installers move to 48 V.
Example 2 — Inverter: 2000 W inverter at 48 V, 3 m one-way
"What size wire for 2000 watt inverter installs?" is one of the most searched DC wiring questions — and the answer always starts with system voltage. Current = 2000 ÷ 48 = 41.7 A. Here voltage drop is easy (even 10 AWG only drops 2.08%), but 10 AWG is rated 40 A — below the 52.1 A continuous-duty requirement. The ampacity gate, not the drop gate, decides: answer 8 AWG copper (55 A, 1.30% drop). Short, high-current inverter cable size decisions are almost always ampacity-limited.
Quick reference: 24V vs 48V wire size
Same load, same distance, different voltage — this is why voltage matters more than anything else in DC cable sizing. For a 20 A load over 10 m one-way at 3% max drop (copper, 75°C, continuous duty): a 24V wire size of 6 AWG is required (2.61% drop), while the 48V wire size for the identical run is only 8 AWG (2.09% drop). Double the volts, roughly two gauges thinner.
Example 3 — RV: 12 V fridge circuit, 8 A, 5 m one-way
At 12 V every tenth of a volt matters. 14 AWG drops 6.7% and 12 AWG drops 4.2% — both fail 3%. Answer: 10 AWG copper (2.66% drop, 40 A ampacity). Camper-van and RV 12 V circuits routinely need thicker wire than intuition suggests; this is exactly what a dedicated 12V wire size calculator is for, while this page covers DC generally.
Solar Panel Wiring Tips
The wire size for solar panels is set by the array's current at its operating voltage over the home-run distance — not by the panel's wattage alone. Use this page as your solar panel wire size calculator: enter the array current, system voltage and one-way roof-to-controller distance above. Get the home run right and the rest is easy.
- Wire for the array voltage, not 12 V by habit. Two 200 W panels in series at ~40 Vmp draw half the current of the same panels in parallel at ~20 Vmp — halving the current quarters the voltage drop for a given wire, or lets you use thinner, cheaper wire. This series vs parallel solar panel wiring choice is the single biggest lever on solar panel wire size.
- Size the home run, not the panel leads. Panel whip leads are short; the expensive run is panels → charge controller (and controller → battery). Measure that one-way distance carefully, including routing around roof edges.
- Use UV-rated PV wire outdoors. Standard THHN in sunlight degrades; PV wire (or wire in UV-rated conduit) is made for decades on a roof.
- Size the controller-to-battery run for the controller's output current (e.g. a 40 A MPPT at 24 V), not the array current — an MPPT steps voltage down and current up. This is the solar charge controller wire size most DIY installers underestimate.
- Keep parallel strings balanced: equal wire lengths to each string so one string doesn't hog current.
RV & Automotive Wiring Tips
- Use stranded wire, not solid. Vibration in vehicles and trailers work-hardens solid copper until it cracks. Marine-grade tinned stranded wire is the gold standard for RV, camper-van and boat DC wiring — and for any camper van wiring where cables flex with the build.
- RV battery cable size is usually set by the inverter, not the drop. Battery-to-inverter feeds are short and carry huge currents: a 2000 W inverter on a 12 V lithium bank pulls ~167 A, which needs 4/0 AWG. Lithium battery cable size should always be rated for the BMS/inverter maximum, since lithium delivers surge current with almost no voltage sag to warn you.
- Car audio follows the same math. Car amplifier wire gauge is just current over distance: a 1000 W amp at 12 V draws roughly 80 A, so the power feed from the battery needs 4 AWG or thicker depending on length — and the ground return should match it.
- The chassis is a conductor — with caveats. Many automotive circuits ground through the chassis, which shortens the copper run. But chassis steel has higher resistance than copper and connections corrode; for high-current or noise-sensitive circuits (audio amplifiers, inverters) run a dedicated negative wire of the same gauge.
- Fuse at the power source. Every positive wire gets a fuse within ~20 cm of the battery or busbar, sized to protect the wire (see fuse section below), not just the load.
- Mind the alternator's real voltage. Automotive "12 V" systems run at ~13.8–14.4 V while charging — size with 12 V nominal for drop calculations (conservative) and rate components for the charging voltage.
- Trailer wiring: brake and charge lines run the full vehicle-to-trailer length; measure bumper to bumper plus slack, and remember the 3% rule for brake controllers.
Copper vs Aluminum & Temperature
Copper is the default for DC wiring: lower resistance, smaller gauges for the same current, and terminals that stay tight. Aluminum is cheaper and lighter — common for long solar farm feeders — but needs roughly two AWG sizes larger for the same performance, anti-oxidant paste on terminations, and connectors rated for aluminum (copper-only lugs on aluminum wire corrode and loosen).
Temperature matters twice. Hot conductors have higher resistance (copper rises ~0.393% per °C), so a wire in a sun-baked conduit or engine bay drops more voltage than the same wire in free air — this calculator corrects resistance for your chosen conductor temperature. Heat also reduces ampacity. When a run passes through hot zones, either select 90°C here or simply go one gauge thicker.
Fuse Sizing for DC Circuits
A fuse protects the wire, not the appliance. The rule: fuse rating ≥ 125% of the load current, and never above the wire's ampacity. This calculator suggests a standard fuse size from that rule, capped at the recommended wire's ampacity.
Place the fuse as close to the power source (battery, busbar, charge controller output) as practical, on the positive conductor. For battery banks, add a main battery fuse rated for the thickest cable leaving the bank. Automotive blade fuses, MIDI/AMI fuses (30–200 A) and ANL/Class-T fuses (100 A+) cover most solar, RV and car-audio DC circuits; use DC-rated fuses — AC-only fuses may not safely interrupt a DC arc.
Frequently Asked Questions
How do I calculate the right wire size for a DC circuit?
Compute your current (amps = watts ÷ volts), measure the one-way wire length, and pick the smallest AWG that passes two tests: its ampacity must cover 125% of a continuous load, and its round-trip voltage drop (2 × I × R × length) must stay under your limit — 3% for critical circuits. This calculator runs both checks automatically.
What is an acceptable voltage drop for DC wiring?
3% for critical circuits (inverters, chargers, starter and ECU feeds, navigation) and up to 10% for non-critical circuits (lights, fans), per marine standard ABYC E-11, which is widely used for RV and off-grid DC work. Sensitive 12 V electronics may misbehave well before 10%, so 3% is the safe default.
Do I double the wire length when calculating DC voltage drop?
Yes. Current flows out on the positive conductor and back on the negative, so both runs drop voltage — the formula uses the round-trip length (2 × one-way length). Forgetting the return run is the most common DC cable sizing mistake. Enter the one-way length in this calculator; it doubles it for you.
What size wire for a 2000 watt inverter?
It depends on system voltage: 2000 W ÷ 12 V = 167 A (needs 4/0 AWG), ÷ 24 V = 83 A (around 2 AWG), ÷ 48 V = 42 A (8 AWG for a short run). Higher voltage means lower current and dramatically thinner wire — enter your exact voltage and length above for the precise answer.
What gauge wire do I need for solar panels?
Size for the array's current at its operating voltage over the one-way run to the charge controller. Example: a 400 W array at 24 V (16.7 A) across 12 m needs 6 AWG copper at 3% drop. Wiring panels in series raises voltage and halves current, which quarters voltage drop — the cheapest way to shrink solar wire size.
Does higher system voltage mean I can use thinner wire?
Yes. For the same power, doubling voltage halves current, and voltage drop is proportional to current — so at double the voltage you can use roughly two AWG sizes thinner, or run twice as far on the same wire. This is why off-grid systems migrate from 12 V to 24 V and 48 V as they grow.
Should I use copper or aluminum wire for DC?
Copper for most solar, RV and automotive work: smaller gauges, better terminations, no special pastes. Aluminum is cheaper and lighter for very long runs (solar farms), but needs about two AWG sizes larger, ampacity derated to 78%, and aluminum-rated connectors with anti-oxidant compound. This calculator supports both.
Can I use regular AC household wire for DC circuits?
Only if it is rated for the voltage, current and environment — and in practice, use wire made for the job: stranded automotive or marine wire for vehicles and boats (vibration cracks solid wire), UV-rated PV wire for outdoor solar. Never use AC-only fuses or breakers on DC; they may fail to interrupt a DC arc.
What happens if my DC wire is too small?
Two failures: the wire overheats — melting insulation and creating a fire risk — and voltage drop starves the load, so inverters shut down, motors run hot and slow, and batteries charge incompletely. Undersized wire wastes power as heat for the entire life of the installation.
How does temperature affect DC wire sizing?
Copper resistance rises about 0.393% per °C, so a hot conductor drops more voltage than a cool one, and heat also lowers ampacity. Wire in sun-baked conduit or an engine bay should be sized at a higher conductor temperature (select 90°C in this calculator) or simply upsized one gauge.
What size fuse should I use for my DC circuit?
Size the fuse to protect the wire: at least 125% of the load current but never above the wire's ampacity, placed close to the power source on the positive conductor. This calculator suggests a standard fuse size with each result. Always use DC-rated fuses — AC fuses may not safely break a DC arc.
Is stranded or solid wire better for DC?
Stranded, for anything that moves or vibrates — vehicles, trailers, RVs, boats. Solid copper work-hardens and cracks under vibration; stranded wire flexes without damage. Marine-grade tinned stranded copper resists corrosion best in damp environments.
What wire size do I need from my RV battery to the inverter?
Inverter feeds are short and high-current, so ampacity usually decides, not voltage drop. A 2000 W inverter at 12 V (167 A) needs 4/0 AWG; the same inverter at 24 V (83 A) needs about 2 AWG. Enter your inverter wattage, battery voltage and one-way cable length above for the exact size, and fuse the positive cable at the battery.
Do solar panels need special wire?
For the outdoor run, yes: use UV- and weather-rated PV wire (or standard wire inside UV-rated conduit) between the array and the point where it enters the building. Indoors, standard stranded copper of the correct gauge is fine. PV wire's thick XLPE insulation is built for decades of sun exposure.
How is this different from a 12V wire size calculator?
A 12V-only calculator fixes the system voltage at 12 volts. This is a general DC wire size calculator: it accepts any DC voltage — 12 V, 24 V, 48 V or a custom value — so one tool covers solar arrays, 24/48 V battery banks, RV house systems and automotive circuits with the same voltage-drop and ampacity math.
Is this calculator accurate enough for boat wiring?
It applies the same ABYC E-11 logic used for marine DC sizing — whether you call it boat wire size or marine cable sizing — ampacity plus a 3% critical / 10% non-critical voltage-drop limit, so it gives correct minimum sizes. For inspected or insured vessels, still have the installation checked against the full ABYC standard by a qualified marine electrician, since bundling, engine spaces and insulation ratings add derating this simplified tool cannot cover.