Are these figures published standards or rules of thumb?

Both, and the page labels which is which. Conductor ampacity, resistance, voltage drop limits, overcurrent sizing factors and device ratings come from NEC, ABYC and NEMA and are labeled as published standards. Depth of discharge, solar derate factors and inverter efficiency are planning conventions with no standards body behind them, and are labeled as conventions.

Why does this calculator sometimes say there is no answer?

Because there genuinely is not one within the published tables. Rather than extrapolating past the end of an ampacity table or inventing a figure to fill a gap, the calculator returns nothing and explains why. A run that is too long for the current at 12 volts needs a shorter run or a higher system voltage, not a made up wire size.

Do I still need an RV technician if I use this?

For DC work many owners do their own installation, and these figures are the ones that work is sized from. Permanent AC wiring, anything connected to the shore power inlet and anything behind the distribution panel is work for a qualified RV technician or a licensed electrician. Sizing a circuit correctly and installing it safely are two different jobs.

Wiring calculator

RV Wire Gauge and Voltage Drop Calculator

Quick answer

Voltage drop is two times the one-way run length times current times the conductor resistance per foot. The doubling is the round trip: current returns on the negative conductor and drops voltage there too.

Result

Smallest adequate conductor 4 AWG copper

Voltage drop 2.57 %

Voltage lost in the run 0.308 V

Conductor ampacity 160 A per ABYC E-11 Published standard

The formula

drop volts = 2 x run length (ft) x amps x (ohms per 1000 ft / 1000)

Halving this by forgetting the return conductor is the single most common RV wire sizing error, and it undersizes the cable by a factor of two.

The figures shown above are computed with these exact inputs: Current 50 A, One-way run length 10 ft, System voltage 12 V, Voltage drop target 3 %, Ampacity table abyc.

What this calculator assumes

Some of these are published standards and some are conventions. They are not the same kind of number, so each one is labeled.

Assumption	Kind	Where it comes from
NEC Chapter 9	Published standard	NEC Chapter 9, Table 8, DC resistance of uncoated stranded copper at 75 C
ABYC E-11	Published standard	ABYC E-11, 105 C insulation, outside engine spaces
Abyc Critical Drop Pct: 3	Published standard	ABYC E-11 voltage drop limit for critical circuits
Abyc Non Critical Drop Pct: 10	Published standard	ABYC E-11 voltage drop limit for non-critical circuits

Components that match this result

Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.

Beginner

TOPDC

TOPDC 4 AWG Battery Cable Pair, 18 in

$11.98

Pure copper with factory-crimped 3/8 inch lugs. A crimped lug from the factory beats a hand-twisted connection every time.

Best for: Short battery to busbar runs.

Check price on Amazon

Beginner

A ABIGAIL

4 AWG Battery Inverter Cable, 2 ft Pair

$20.99

A 2 foot pair suits an inverter mounted close to the bank, which is where an inverter should be.

Best for: Inverter to battery on a short run.

Check price on Amazon

Frequently asked questions

How does the wire gauge and voltage drop calculation work?: drop volts = 2 x run length (ft) x amps x (ohms per 1000 ft / 1000). Halving this by forgetting the return conductor is the single most common RV wire sizing error, and it undersizes the cable by a factor of two.
Are these figures published standards or rules of thumb?: Both, and the page labels which is which. Conductor ampacity, resistance, voltage drop limits, overcurrent sizing factors and device ratings come from NEC, ABYC and NEMA and are labeled as published standards. Depth of discharge, solar derate factors and inverter efficiency are planning conventions with no standards body behind them, and are labeled as conventions.
Why does this calculator sometimes say there is no answer?: Because there genuinely is not one within the published tables. Rather than extrapolating past the end of an ampacity table or inventing a figure to fill a gap, the calculator returns nothing and explains why. A run that is too long for the current at 12 volts needs a shorter run or a higher system voltage, not a made up wire size.
Do I still need an RV technician if I use this?: For DC work many owners do their own installation, and these figures are the ones that work is sized from. Permanent AC wiring, anything connected to the shore power inlet and anything behind the distribution panel is work for a qualified RV technician or a licensed electrician. Sizing a circuit correctly and installing it safely are two different jobs.

Researched guidance, not professional advice. These results are planning figures from published standards and manufacturer specifications. Never exceed a conductor's rated ampacity, fuse every positive conductor close to the battery, never run a generator in an enclosed space because carbon monoxide is lethal and odorless, and have permanent AC wiring done by a qualified RV technician or licensed electrician.