DIY RV Tech logo DIY RV TechKnow your RV
DIY RV Tech · Free Tools & Resources

Free RV Resources

Practical RV tools, calculators, checklists, and owner-focused resources to help you understand your RV and maintain it with confidence.

Know your RV. Protect your trip.DIYRVTech.com
Start Here

Get the Free Pre-Trip Inspection Checklist

Join the DIY RV Tech email list and get the free checklist, plus future free resources, RV tips, product notifications, and training updates.

Send Me The Free Checklist Check RV Recalls
Free Resource Use Disclaimer
Read Before Using These Tools

Educational Tools Only

The calculators, reference charts, and printable resources on this page are provided for general RV owner education and planning only. They are not a substitute for manufacturer instructions, product labels, RVIA standards, the National Electrical Code, or inspection by a qualified RV technician or electrician.

Use at your own risk: DIY RV Tech does not guarantee the accuracy, completeness, or suitability of these free tools for your specific RV, equipment, wiring, batteries, tires, fuses, or travel situation. You are responsible for verifying all results before taking action. If a task involves safety, propane, 120V AC power, battery banks, high current DC circuits, structural components, or anything beyond your comfort level, stop and consult a qualified professional.
RV Electrical Calculators
Ohm's Law + Wattage + Battery Planning

Free RV Electrical Calculators

Use these tools for basic RV electrical planning and owner safety checks. Work through Ohm's Law, estimate battery runtime, check voltage drop, decode tire DOT dates, estimate battery state of charge, and review common RV electrical references.

Safety note: These calculators are for education and planning only. Always verify loads using the device data plate or manual. RV electrical work can be dangerous.
E = I × RP = E × II = P ÷ ER = E ÷ I
Ohm's Law Calculator

Calculate Voltage, Current, Resistance, Or Wattage

Choose the result you need, then enter the known values. This one tool handles the same amp-draw-from-wattage calculation without needing a separate calculator.

E = I × R   |   P = E × I   |   I = P ÷ E   |   R = E ÷ I
How to use it:
  • To calculate voltage / E: choose Voltage / E, enter amperage and resistance. Example use: finding voltage drop across a known resistance.
  • To calculate amperage / I from wattage: choose Amperage / I, enter voltage and wattage, and leave resistance blank. Example: 1,500 watts ÷ 120 volts = 12.5 amps.
  • To calculate amperage / I from resistance: choose Amperage / I, enter voltage and resistance, and leave wattage blank.
  • To calculate resistance / R: choose Resistance / R, enter voltage and amperage.
  • To calculate wattage / P: choose Wattage / P, enter voltage and amperage. Example: 120 volts × 10 amps = 1,200 watts.

Calculator

Result—

Choose a calculation and enter the known values.

Battery Runtime Calculator

Battery Runtime Calculator

Estimate how long a battery bank can run a load. Use amp draw for 12V DC loads or wattage for 120V inverter loads.

Runtime = Usable Battery Capacity ÷ Load
How to use it:
  • Battery Bank Capacity: enter the total amp-hours of the battery bank. Example: two 100Ah batteries = 200Ah.
  • Battery Voltage: choose the battery bank voltage, usually 12V for many RV battery systems.
  • Usable Capacity: enter the percentage you plan to use. A conservative lead-acid estimate is 50%; lithium may be higher if your battery manual allows it.
  • Load in amps: use this for 12V DC loads such as lights, fans, furnace blowers, and water pumps.
  • Load in watts: use this for 120V AC loads powered through an inverter. Enter inverter efficiency so the calculator can account for conversion loss.

Real-world runtime may be lower because of inverter losses, battery age, temperature, wiring, and startup surges.

Estimate Runtime

Result—

Enter battery capacity and load.

Voltage Drop Calculator

Voltage Drop Calculator

Estimate voltage drop for copper wire using one-way circuit length, amperage, system voltage, and wire gauge.

Voltage Drop = Amps × Round-Trip Feet × Wire Resistance
How to use it:
  • System Voltage: choose the circuit voltage. Voltage drop matters more on low-voltage DC circuits such as 12V systems.
  • Load Current: enter the amps the load draws. If you only know watts, use the Ohm's Law calculator first: choose Amperage / I and enter wattage plus voltage.
  • One-Way Wire Length: enter the distance in feet from the power source to the load. The calculator automatically doubles it for the round-trip circuit path.
  • Copper Wire Gauge: choose the wire size. A lower AWG number is a larger wire and usually has less voltage drop.
  • Result: lower is better. A common planning target is about 3% voltage drop, but always follow applicable codes, manufacturer instructions, and safe wiring practices.

Estimate Voltage Drop

Result—

Enter amperage, length, and wire gauge.

Propane & Water System Calculators
Interactive Tools

Free Propane & Water Calculators

Use these calculators to plan your propane supply and sanitize your fresh water system correctly. Results update instantly as you enter your information.

Planning tools only: Propane estimates are based on appliance rated BTU and hours entered. Actual consumption varies with temperature, altitude, and appliance age. Bleach formula uses standard 5.25% unscented household bleach. Always verify with your RV owner's manual.
Propane Duration Calculator

How Long Will Your Propane Last?

Select your tank size, set the gauge level, and turn on the appliances you are running. Your estimated days remaining updates instantly.

BTU Available ÷ BTU Per Day = Days Remaining
How to use it:
  • Tank size: select a common size or type your gallons directly.
  • Gauge level: drag the slider to match your propane gauge reading.
  • Appliances: toggle on each appliance you are running and enter how many hours per day it runs. Controls expand when toggled on.
  • Result: green = 7+ days · yellow = 3–6 days · red = under 3 days. Always carry extra on long trips.

1 gallon of propane = 91,502 BTU. Tank capacities: 20 lb ≈ 4.73 gal · 30 lb ≈ 7.1 gal · 40 lb ≈ 9.5 gal · 100 lb ≈ 23.6 gal.

Your Tank

Gauge level100%

Select a tank size or enter gallons above.

Appliances In Use

🔥
Furnace
25,000 BTU/hr
🚿
Water Heater
10,000 BTU/hr
🍳
Range / Cooktop
~8,500 BTU per burner
🧊
Absorption Refrigerator
1,600 BTU/hr — runs continuously
♨️
Propane Heater / Fireplace
25,000 BTU/hr
Estimated Days Remaining
—
days

Enter your tank size and toggle on the appliances you are running.

—BTU / day
—gallons avail.
—total BTU
Daily BTU Breakdown
Water Tank Sanitization Calculator

How Much Bleach Do You Need?

Enter your fresh water tank size in gallons and get the exact amount of unscented household bleach to sanitize your system. Results update as you type.

¼ cup unscented household bleach per 15 gallons
Critical reminders before you start:
  • Bypass the water heater first. Bleach damages aluminum anode rods and causes rotten egg odor when heated through an active water heater.
  • Unscented bleach only — standard 5.25% sodium hypochlorite. Scented or splash-less bleach contains additives that are not safe for drinking water lines.
  • No hot water when mixing or flushing. Use cold fresh water only.
  • Let it sit 4–24 hours after running to all faucets, then drain and flush completely until no bleach smell remains.
  • Only after flushed: remove water heater bypass, refill, then turn heater on.

Enter Your Tank Size

Bleach Needed
—
cups
—fluid oz
—tablespoons
—teaspoons
Formula: ¼ cup per 15 gallons · 5.25% unscented household bleach
RV Tire DOT Date Checker

Decode Your Tire Date Code

Most RV tire sidewalls include a DOT date code showing the week and year the tire was manufactured. This tool helps you decode the last four digits.

How to use it:
  • Find the DOT code: look on the tire sidewall for the DOT marking. The date code is usually the last four digits.
  • Enter four digits: the first two digits are the manufacturing week and the last two digits are the manufacturing year. Example: 3521 means week 35 of 2021.
  • Check tire age: the tool estimates the tire's age from the manufacturing week.
  • Verify before replacing: age is only one factor. Inspect for cracking, bulges, uneven wear, sidewall damage, and follow the tire/RV manufacturer's guidance.

Check Tire Age

Result—

Enter the last four digits of the DOT date code.

Battery State-Of-Charge Reference

Estimate Battery Charge From Resting Voltage

Use this as a rough reference for resting battery voltage. Battery voltage should be checked with the battery at rest, not while charging or under a heavy load.

How to use it:
  • Choose battery type: select flooded lead-acid, AGM, or lithium/LiFePO4.
  • Enter resting voltage: measure at the battery terminals after the battery has rested. Recent charging or heavy loads can make the reading misleading.
  • Read the estimate: the tool gives an approximate state of charge range and a plain-language note.
  • Use manufacturer specs: lithium batteries and some AGM batteries have different voltage curves. Always verify with the battery manual or BMS/app when available.

Estimate Charge

Result—

Enter resting voltage for a 12V battery bank.

Printable RV Emergency Info Card
Free Printable

Build A Quick Emergency Information Card

Fill in the fields below, print the card, and keep a copy in your RV. This can help family, campground staff, roadside assistance, or emergency responders find important information quickly.

Suggested use:
  • Print one copy for the RV and one copy for your tow vehicle or motorhome cab.
  • Review and update it before each travel season.
  • Do not include sensitive information you would not want visible if the card is found by someone else.
Privacy note: The Emergency Info Card Builder runs in your browser only. DIY RV Tech does not save, retain, transmit, record, use, or sell any information you type into this card builder. The information remains on your device unless you print it or choose to share it.

Card Information

Preview

DIY RV Tech Emergency Info Card
Fill in the form and click Build Card.
Common RV Fuse Color Reference
Electrical Reference

Common Automotive Blade Fuse Colors And Amp Ratings

Use this as a quick visual reference for common automotive-style blade fuses found in many RV 12V fuse panels. Always match the amp rating required by the RV manufacturer, circuit label, appliance manual, or original fuse rating.

Important: Never install a larger fuse to “fix” a blowing fuse. A fuse protects the wiring. Replacing a fuse with a higher amp rating can overheat the wire and create a fire hazard. If a fuse keeps blowing, find and repair the cause.
1
Black
1 amp
2
Gray
2 amps
3
Violet
3 amps
4
Pink
4 amps
5
Tan
5 amps
7.5
Brown
7.5 amps
10
Red
10 amps
15
Blue
15 amps
20
Yellow
20 amps
25
Clear
25 amps
30
Green
30 amps
40
Orange
40 amps

Fuse color standards are commonly used, but you should always verify the number printed on the fuse body and the rating specified for the circuit. This chart is a visual owner-reference only.

Common RV Electrical Loads
Reference Guide

Common Wattages For Everyday RV Devices

Use this as a rough planning guide. Actual wattage varies by brand, size, condition, and startup surge. Always check the label or manual on your specific device.

Device / LoadTypical Running WattsPlanning Notes
LED light fixture3–10 WSmall draw, but multiple fixtures add up.
Phone charger5–20 WUsually low draw.
Laptop charger45–100 WCheck the charger label.
TV50–150 WLarger TVs use more power.
Roof vent fan20–40 WSpeed setting matters.
RV water pump60–120 WIntermittent load, not usually continuous.
Furnace blower80–150 WMajor overnight battery draw in cold weather.
Propane refrigerator controls5–20 WControls only; not electric cooling mode.
Absorption refrigerator on electric300–600 WCan be a heavy continuous AC load.
Residential refrigerator100–250 WStartup surge may be higher.
Microwave1,000–1,500 WHigh draw; inverter and battery bank must be sized correctly.
Coffee maker600–1,200 WShort run time, high draw.
Toaster800–1,500 WHigh draw on a 120V circuit.
Hair dryer1,200–1,875 WOften near the limit of a 15A circuit.
Electric space heater750–1,500 WA 1,500W heater draws about 12.5A at 120V.
Electric water heater element1,200–1,500 WLarge AC load.
13,500 BTU roof air conditioner1,200–1,800 WStartup surge can be much higher.
Learn The System

Want Printable Step-By-Step Checklists?

The RV Preventive Maintenance Action System gives you 50+ pages of printable maintenance checklists designed to work alongside the book chapters.

View The Action SystemLearn About The Book
Suggest A New Tool Or Resource
We're Listening

Don't See What You Need?

New tools are added based on what real RV owners are asking for. If there's a calculator, reference guide, or resource that would help you maintain your RV — send it in.

Tell me the system (electrical, propane, water, tires, A/C, etc.), what the tool should do, and why it would help. Every suggestion is reviewed personally.

Suggest A Tool Or Resource

Goes directly to Marvin Kennedy — no forms, no bots. marvin@DIYRVTech.com