The RV Electrical Load Calculator helps users estimate electrical loads by converting watts to amps, sizing generators, and applying Ohm's Law for voltage drop calculations. This tool addresses common issues such as breaker trips and overheating due to incorrect load estimation, providing a foundation for safe electrical planning in RVs.
Generated from this page. Always verify technical specs.
Load calculation and verification usually requires these tools.
| Tool | Why You Need It |
|---|---|
| 🔧 Best Multimeter for RV | Verify voltage under load |
| 🔧 Best RV Generators | Compare models for your needs |
| 🔧 Best RV EMS Systems | Monitor voltage when running on generator |
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This calculator helps RV owners safely estimate: Watts ↔ Amps conversions, Ohm's Law (V = I × R), Generator sizing for air conditioners, and Electrical load headroom on 30A and 50A service. Improper load estimation is one of the most common causes of breaker trips, overheating wires, and voltage-related AC failures. Use for planning—not as a substitute for licensed electrical inspection.
RV electrical systems can be complex. Every appliance draws watts, and every circuit has a limit. This tool helps you plan your electrical load, size generators correctly, and understand voltage drop before problems occur. Use it to ensure you aren't overloading your 30A or 50A service, which is a common cause of breaker trips and HVAC failures.
Whether you're planning for a new appliance or troubleshooting an existing issue, these calculations provide the baseline you need for a safe and reliable setup. Note: Always use a multimeter for field verification. See how to test pedestal voltage for step-by-step instructions.
Formulas: Amps = Watts ÷ Volts | Watts = Amps × Volts
At 120V (standard RV shore power), 1,800W = 15A. A 13,500 BTU AC typically draws 12–15A running; a 15,000 BTU unit may draw 15–18A. Use this converter when you know appliance wattage and need to check amp draw against your breaker or service capacity—or when you know amps (e.g., from an AC nameplate) and need wattage for generator sizing.
Common RV appliance wattages: microwave 600–1,200W, electric water heater 1,300–1,400W, space heater 1,500W, residential fridge 100–200W, TV 50–150W. Add them up and convert to amps to see if you're within 30A (3,600W) or 50A (~12,000W). See how many amps RV AC uses for typical draws by unit size. The load management checklist helps you stagger high-draw appliances.
Ohm's Law relates voltage (V), current (I in amps), and resistance (R in ohms): V = I × R. Use it for voltage drop calculations—e.g., how much voltage is lost over a long extension cord or undersized wiring.
Example: A 50-foot 14 AWG copper cord has roughly 0.25Ω resistance per conductor (round-trip ~0.5Ω). At 15A, voltage drop = 15 × 0.5 = 7.5V. If the pedestal reads 118V, you might see only 110V at the RV—marginal for AC. A 10 AWG cord has lower resistance and less drop. See RV wire gauge load guide for ampacity by AWG. Never use household extension cords for RV shore power; use RV-rated cords of proper gauge.
This calculator solves for voltage when you know amps and resistance. Enter amps (e.g., 15 for AC) and resistance (in ohms), then click Calculate Voltage to see the drop. Use it to plan cord length and gauge before you camp.
RV air conditioners draw 2–3× running amps at startup. A 15A-running AC may pull 30–45A briefly when the compressor kicks on. That surge determines minimum generator size—not running watts. Portable generators advertise both running and surge (peak) wattage; you must size for surge.
Enter your AC's running amps (from the nameplate or manual—typically 12–15A for 13,500 BTU, 15–18A for 15,000 BTU) and a surge multiplier. Use 2 for a conservative estimate; 2.5 if your AC is older or you're in hot weather. The calculator estimates recommended generator wattage. Add 500W headroom for fridge, lights, and converter. See best generator for 15,000 BTU RV AC and generator sizing guide.
A soft-start kit reduces surge by roughly 60–70%, allowing smaller generators to run AC. With soft start, a 2,200W inverter generator can often run a 13,500 BTU AC that would otherwise need 3,500W+. See best soft start for RV AC.
30 amp RV service delivers 3,600W total (30A × 120V). 50 amp delivers two legs of 120V—up to ~12,000W combined. Your heaviest load is usually the AC. Use the Watts ↔ Amps converter above to verify: 1,800W running = 15A. Add microwave (1,000W ≈ 8A), fridge (150W ≈ 1.3A), and lights—you can exceed 30A quickly.
Real-world scenario: You're on 30A. AC runs (1,800W). You start the microwave (1,000W). Total 2,800W—still under 3,600W. But when the AC compressor cycles off and on, startup surge adds 1,800–2,700W briefly. Surge + microwave can trip the breaker. Solution: stagger. Run AC, let it stabilize, then use microwave for short bursts. Or add a soft-start kit to reduce AC surge.
50A rigs have more headroom but can still overload if you run dual ACs, microwave, water heater, and space heater simultaneously. Use this calculator to add up your typical loads. See 30 vs 50 amp and load management checklist. If your AC breaker keeps tripping, load math is the first check.
| Service | Total Watts | Typical AC + Basics |
|---|---|---|
| 30A | 3,600W | One AC (~1,800W) + fridge + lights. Stagger microwave. |
| 50A | ~12,000W | Dual AC + microwave + water heater. More headroom. |
Watts ↔ Amps: Use when you're adding up appliance loads (e.g., "Can I run AC and microwave on 30A?") or when you have a nameplate amp rating and need wattage for generator sizing. Example: AC nameplate says 14A—14 × 120 = 1,680W running.
Ohm's Law: Use when planning extension cord length, diagnosing voltage drop, or understanding why voltage sags when AC runs. Example: 50 ft of 12 AWG has ~0.16Ω per conductor; at 15A round-trip drop ≈ 4.8V.
Generator estimator: Use when buying or sizing a generator for AC. Enter running amps from your AC's nameplate or manual. Surge multiplier 2 is conservative; 2.5 for hot weather or older units. The result is minimum generator wattage—add 500W for other loads.
Ignoring startup surge: AC draws 2–3× running amps at startup. Sizing a generator for running watts only will fail. Always use surge in the generator estimator.
Forgetting other loads: Fridge, converter, lights, TV add 200–500W. Water heater adds 1,300W. Add them to your total before comparing to 3,600W (30A) or 12,000W (50A).
Using peak wattage for appliances: Microwaves often list "cooking power" (e.g., 1,000W) but draw 1,200–1,400W from the outlet. Use the higher number for safety.
Long cord, thin gauge: A 100-foot 14 AWG cord drops significant voltage at 15A. Use 10 AWG for 30A runs over 25 feet. See wire gauge guide.
15,000 BTU AC drawing 15 amps running:
With a soft-start kit, surge drops to ~1,200–1,800W—allowing a 2,500–3,000W generator. See best generator for 15,000 BTU RV AC and how many amps RV AC uses. Protect your AC with an EMS or surge protector—low voltage damages compressors. See RV AC low voltage problems.
When your AC isn't cooling or your breaker keeps tripping, run the numbers first. (1) Use Watts ↔ Amps to add up your loads. AC (1,800W) + microwave (1,200W) + fridge (200W) = 3,200W = 26.7A. On 30A you're close—any surge trips the breaker. (2) Use the generator estimator if you're on genny: 15A running × 2 surge × 120V = 3,600W minimum. If your generator is 3,000W, it may fail to start the AC. (3) Use Ohm's Law if voltage sags: long cord or weak pedestal? Calculate the drop. (4) Verify with a multimeter—see how to test RV outlet. Most "AC not cooling" and "breaker tripping" issues are load or voltage—not mechanical failure.
Scenario 1: 30A rig, one 13,500 BTU AC. AC runs fine alone. Breaker trips when you start the microwave. Math: 1,800W + 1,200W = 3,000W. Add AC startup surge (brief 2,500–3,500W) and you exceed 3,600W. Fix: stagger use, or add soft start to reduce AC surge.
Scenario 2: 50A rig at 30A pedestal with adapter. You expect full capacity. Adapter only changes plug shape—you're still limited to 3,600W. One AC + basics is fine; dual ACs will trip. Use the calculator to verify.
Scenario 3: Voltage reads 118V at pedestal, 108V when AC runs. Ohm's Law: 10V drop at 15A = 0.67Ω resistance. Likely long or thin cord, or weak park wiring. Use heavier cord or move to a closer site. Below 108V—shut off AC. See what voltage damages RV AC.
Long extension cords and undersized wiring cause voltage drop. The formula V = I × R tells you how much. At 15A, a 100-foot 14 AWG cord (round-trip resistance ~1Ω) drops 15V. Pedestal at 118V → 103V at the RV. Below 108V risks compressor damage. See RV AC low voltage problems and what voltage damages RV AC.
Copper wire resistance per 1,000 feet (approximate): 14 AWG ~2.5Ω, 12 AWG ~1.6Ω, 10 AWG ~1Ω. Round-trip (hot + neutral) doubles that. A 50-foot 14 AWG cord: 0.05 × 2.5 × 2 = 0.25Ω round-trip. At 15A: 15 × 0.25 = 3.75V drop. A 100-foot 14 AWG: ~7.5V drop. Use the Ohm's Law calculator with your cord length and gauge to estimate.
If you need a long cord, use heavier gauge: 10 AWG for 30A, 8 AWG or larger for 50A. See wire gauge guide and best RV extension cords. An EMS or surge protector with voltage display lets you see real-time voltage—if it drops when AC runs, you have a weak circuit or undersized cord. Campground infrastructure varies; older parks and peak-hour demand often cause voltage sag. An EMS cuts power when voltage drops below 108V—protecting your compressor. See EMS vs surge protector.
Generators list two wattage numbers: running (continuous) and surge (peak). Surge lasts a few seconds when motors start. An AC compressor needs surge to overcome inertia. If the generator can't deliver it, the AC may hum but not start—or the generator may trip. Sizing for running watts only is the most common generator mistake.
Example: 13,500 BTU AC, 14A running. Running watts = 14 × 120 = 1,680W. Surge ~2× = 3,360W. A 3,000W generator might fail; a 3,500W unit with 4,000W+ surge usually works. Add 500W for fridge and lights → 4,000W minimum. Inverter generators often have strong surge relative to running; conventional generators may sag under sudden load. See best generator for 15K BTU AC. At high elevation, generator output drops—oversize by 10–15% above 5,000 feet. See generator sizing guide.
This tool assists estimation and does not replace licensed electrical inspection. Use for planning and education. For actual wiring, modifications, or generator installation, consult a qualified electrician or RV technician.
See RV electrical systems guide, electrical setup for beginners, and how to test RV outlet with multimeter. For AC not cooling or breaker tripping, verify load and voltage before assuming mechanical failure.
Once you've run your numbers: (1) Verify voltage at the pedestal with an EMS or surge protector that has a display—or a multimeter. (2) If generator sizing, compare best RV generators—inverter models produce cleaner power for AC compressors. (3) If on 30A, consider a soft-start kit to reduce AC surge.
Inverter generators produce clean sine wave power; conventional generators produce "dirty" power that can stress electronics. For AC compressors, inverter power often means cooler running and longer life. The wattage math is the same—use this calculator for both. Inverter units typically have strong surge ratings; a 2,200W inverter may have 2,200W surge, while a 3,500W conventional may have 4,500W surge. Check the spec sheet. With a soft-start kit, a 2,200W inverter can often run a 13,500 BTU AC. Without soft start, plan 3,500W+. See best RV generators for inverter vs conventional comparison.
When you're off grid, generator sizing is critical. You can't "add another circuit"—you're limited to what the generator delivers. Use the generator estimator, then add every load you'll run: AC, fridge, lights, water pump, converter (battery charging). A 3,500W generator might run AC + fridge + basics, but add microwave and you're over. Stagger. Consider solar for daytime loads to reduce generator runtime. See generator sizing for elevation and temperature derating. An EMS between generator and RV protects against generator voltage fluctuations—some units produce unstable voltage under varying load.
This calculator drives informed purchases. Pair it with:
Keep these formulas handy for quick mental math:
| Appliance | Typical Watts | Amps @ 120V |
|---|---|---|
| 13,500 BTU AC (running) | 1,500–2,000 | 12–17 |
| 15,000 BTU AC (running) | 2,000–2,500 | 17–21 |
| AC startup surge | 2,500–4,500 | 21–38 |
| Microwave | 600–1,400 | 5–12 |
| Electric water heater | 1,300–1,400 | 11–12 |
| Space heater | 1,500 | 12.5 |
| Residential fridge | 100–200 | 1–2 |
| TV + laptop | 150–300 | 1–2.5 |
Add your loads and compare to 3,600W (30A) or 12,000W (50A). Stagger high-draw appliances. See load management checklist.
Troubleshooting: RV AC Not Cooling · Low Voltage Problems · Breaker Keeps Tripping
Electrical: Generator Sizing · 30 vs 50 Amp · Test Pedestal Voltage · Load Management Checklist
Protection: Best Surge Protector for AC · EMS vs Surge
HVAC: How Many Amps RV AC Uses · Best Generator for 15K BTU AC
Amps = Watts ÷ Volts. At 120V, 1,800W = 15A. Use our calculator. See generator sizing and 30 vs 50 amp for load limits.
15A × 120V = 1,800W running. Startup surge ~2× = 3,600W. Minimum 3,500W generator. Use our generator estimator. See best generator for 15K BTU AC.
A multimeter verifies voltage at the pedestal and outlet—essential for diagnosing low voltage and load issues. Use our calculator to plan; use a multimeter to verify. See how to test RV outlet with multimeter.
No. This tool assists estimation for planning. Actual wiring and installation require a licensed electrician or RV technician.
If you're diagnosing RV electrical or appliance problems, these guides may help:
RV Breaker Keeps Tripping | RV Generator Won't Start | RV Shore Power Not Working | RV Converter Not Charging | RV Inverter Troubleshooting | RV Outlets Not Working | RV Microwave Not Working | RV Refrigerator Not Cooling | How To Test RV Outlet | Best RV EMS
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This guide is educational and not a substitute for licensed electrical inspection.
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Last updated: March 2026 · Reviewed for technical accuracy