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Free RV calculators · no app, no login

Every number
your RV needs.

Save your rig once. Get battery, solar, towing, tank and trip numbers from calculators that show their work and already know your setup.

Browse all calculators How it works
  • Published specs and standards, cited
  • Remembers your rig and your truck
  • No login, ever
My Rig · Rig 1 Free
RV type
Chemistry
Power — nights  
Water — days  

Enter your battery bank and the nights off-grid update as you type.

Full calculator with gray and black tanks →

How it works

  1. 1

    Add your rig

    Type, batteries, water and people. Thirty seconds, saved on your device.

  2. 2

    Open any calculator

    Your numbers are already filled in. Change one, see everything update.

  3. 3

    Upgrade by the numbers

    Solar, batteries, generator, hitch: see what each one would change in your result before you buy it.

The toolbox

Every calculator, grouped the way you camp

Set up your rig once and every tool starts from it.

Power & Electrical

Batteries, solar, inverters, generators and shore power, all reading the same bank.

RV Power Budget Your appliances → watt-hours per day. The number every other power tool starts from. Ready for your rig Battery Runtime How long your bank runs one load or a whole night, by chemistry, with inverter losses counted. Ready for your rig Battery Bank Size Nights off-grid you want → the amp-hours you need, in lithium or lead-acid. Ready for your rig RV Solar Sizing Panel watts for your daily use, derated for a flat roof, and whether solar or the bank runs out first. Ready for your rig Inverter Size Continuous and surge watts for what you run together, and whether your batteries can feed it. Ready for your rig Generator Size What size runs your air conditioner, and when a soft start does the job of a bigger generator. Ready for your rig Generator Fuel & Runtime Gallons per hour at your load → hours per tank and dollars per day. Ready for your rig 30 A / 50 A Shore Power What runs together on your pedestal before the breaker trips, on 30 A, 50 A and adapters. Ready for your rig Battery Charge Time Hours to refill from a generator, converter, solar or the alternator, absorption phase included. Ready for your rig AC on Batteries Whether your bank, inverter and soft start can run the air conditioner, and for how many hours. Ready for your rig Lithium vs AGM Usable capacity, weight and cost per usable kWh, for the number of nights you camp each year. Ready for your rig 12 V Wire Size Gauge for the amps and run length from NEC and ABYC tables, with voltage drop and the fuse. Ready for your rig Battery Voltage → Charge Resting voltage to state of charge for lead-acid and lithium, from the makers’ tables. Printable. Ready for your rig

In the works Portable Power Station

Water & Tanks

Fresh, gray and black: how long they last and how to look after them.

Boondocking Days How long fresh, gray and black last for your crew, and which tank ends the trip. Ready for your rig Water Heater Showers per tank, recovery time, and what tankless changes. Ready for your rig Sanitize Fresh Tank Bleach for your tank size, the soak time and the rinse, in spring or after storage. Ready for your rig Winterize Antifreeze gallons for your rig and a printable checklist that doesn’t skip the water heater. Ready for your rig

Propane & Climate

Cylinders, furnaces and air conditioners, sized from your rig and the weather.

Propane Duration Furnace, water heater, fridge and stove → days per cylinder at the temperature you’re camping in. Ready for your rig Heater Sizing Furnace BTU or electric heater watts for your rig, and how much heat 30 A can carry. Ready for your rig Air Conditioner Sizing BTU for your length and climate, and whether a second unit fits your shore power. Ready for your rig

Weights & Towing

The four checks that keep a rig inside its ratings, read from your stickers.

Can My Truck Tow This? Tow rating, payload, GCWR and hitch: all four checks, pass or fail, with the margin in pounds. Ready for your rig Tongue & Pin Weight Measure it with a bathroom scale and a board, check the 10 to 15% band, then move cargo to fix it. Ready for your rig CAT Scale Ticket Three weigh-ins → tongue weight, axle loads and every margin, saved to your rig. Ready for your rig RV Loaded Weight Dry weight plus water, batteries, gear and dealer add-ons, against your GVWR and cargo capacity. Ready for your rig Weight Distribution Hitch Whether you need one and which bar rating, sized from your tongue weight plus bed cargo. Ready for your rig Brake Controller Whether your state and your truck call for one, which type, and how to set the gain. Ready for your rig

In the works RV Tire Pressure

Trip & Cost

What a trip costs in fuel, nights and food, and how it compares with a hotel.

Trip Fuel Cost Distance, the MPG your rig gets and today’s price, to what the drive costs. Ready for your rig Trip Cost vs Hotel Fuel, campground nights, food and tolls, against the same trip by car and hotel or by air. Ready for your rig

In the works Drive Time · Cost of Ownership · Leveling

Guides

When the answer isn't a number

All guides →
Reference Find your RV's numbers Every label, plate and sticker the calculators ask about: where it is, what each line means, and which lines to ignore. Diagnose Why does my trailer sway? Tongue weight, speed, tires, hitch: a decision table built from readings you can take on your own rig. Checklist De-winterizing checklist The spring steps in order, the reverse of winterizing plus the sanitize. Printable.

My Rig

One rig. Every system.
All connected.

Save your batteries, solar, generator, tanks, weights and tow vehicle once. Then every calculator on the site starts from your numbers, and My Rig shows which system runs out first.

Shopping? Save three trailers and see which ones your truck can tow, with all four checks side by side.

Open My Rig
My Rig 2022 Grand Design Imagine Travel trailer · 29 ft
27/28
calculators ready for this rig

Generator Fuel & Runtime is waiting on generator

Off-grid limit Water · 6.5 days
  1. Power 400 Ah lithium · 600 W solar · 2,000 W inverter
  2. Water Fresh 52 · Gray 82 · Black 45 gal
  3. Climate 13,500 BTU AC · soft start · 30,000 BTU furnace
  4. Weights GVWR 8,495 · scaled 7,760 lb
  5. Truck F-250 · payload 2,462 lb · tows 15,000 lb

Example rig. Save yours in the card at the top and this becomes your rig.

Math you can check

The numbers come from published sources: NEC and ABYC conductor tables, the federal weight-label rule, manufacturer data sheets and NASA and NREL solar data. Each page lists its sources, and every result has a “show the math” breakdown.

Limits before numbers

An overloaded truck should never come back as “fine”. These calculators flag GCWR, payload, axle and inverter limits in pounds and amps, and say which one you hit first.

Recommendations the math picks

When a result suggests a product, it's the one the math justifies, and we say so when the gear you already own is enough. Some links earn us a commission; that never changes the numbers.

Pinned to the published figures

  • 440 Ahfour 6 V golf-cart batteries, at 12 V
  • 2,560 Whtwo 100 Ah lithium batteries
  • 1.9 kWh/day600 W flat on the roof
  • 4.7 galin a 20 lb cylinder, about 430,000 BTU
  • 3,600 Won a 30 A pedestal; 12,000 W on 50 A

Every engine on the site is tested against these before a page ships. How the math is checked → Report a math error