Made with in our van.

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Van Electrical Calculator

12V DC
LOADName of the appliance. CUR
(A)AVERAGE CURRENT (in amps) drawn during operation. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(A)AVERAGE CURRENT (in amps) drawn during operation. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.


120V AC
LOADName of the appliance. PWR
(W)MAX POWER (in watts) of the load. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(Ah)[(POWER/12) x HOURS] / 0.85
INVThis column is used to size the inverter. Check all the appliances that you plan on using simultaneously. Note that the biggest load is automatically selected by the calculator. PWR
(W)MAX POWER (in watts) of the load. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(Ah)[(POWER/12) x HOURS] / 0.85
INVThis column is used to size the inverter. Check all the appliances that you plan on using simultaneously. Note that the biggest load is automatically selected by the calculator.


Battery Type

Your Type


1- Size Your Main Components
Use the calculator above
Daily Energy Usage

? Ah

Battery Bank

? Ah

Solar Panels

? W

Solar Charger


Alternator Charge

? A

Shore Charger

? A


? W

Manual Mode Enabled.
Bold options = automagic values.
2- Size Your Wires, Fuses & Breakers
+ Wire Lengths & Terminals Calculator

Appropriate wire gauge (AWG) varies with length & load and, therefore, is unique to each installation. Our wiring diagram automatically sizes the wire gauge, fuses & breakers to ensure that your own system is safe and performs as it should. Bonus: it also calculates all the wire lengths & terminals that you'll need by type/gauge, which will make STEP 3 (customize your items list) super easy to complete. No other diagram does this!

3- Customize Your Items list

Fill these tables per your wiring diagram:




Cost EstimateIncludes everything on your Items List, except the 12V & 120V loads (appliances) and Tools. Prices on Amazon change frequently, so our estimate is subject to change.


Items List

The list below defines your entire electrical system. Click on "ADD ITEMS TO AMAZON CART" section-by-section; make sure that all the items are valid (links to Amazon products sometime change, please let us know if that's the case!), and make sure all items are in stock at the moment.

# Item Description Quantity View on Amazon
1 Terminal Fuse Block with Fuse 250A Blue Sea (Catastrophic Fail Safe. Connects directly to battery post.) 1 View
2 System Switch Blue Sea (Main System Switch) 1 View
3 Bus Bar (250A, 4 studs) Blue Sea 2 View
4 Cover for Bus Bar (for 250A 4 studs) Protect the Bus Bar 2 View
5 40A Breaker/Switch, Surface Mount Between Fuse Block and Bus Bar 1 View
6 Fuse Block (12 circuits) Blue Sea (12V Distribution Panel) 1 View
7 Fuses Kit Assorted Fuses (2A 3A 5A 7.5A 10A 15A 20A 25A 30A 35A) 1 View
8 Battery Monitor Victron BMV-712 with BlueTooth 1 View
# Item Description Quantity View on Amazon
1 Heat Shrink Butt Connector, Ancor Marine To connect to Loads (75 Pack Kit) 1 View
2 Heat Shrink Disconnect, 10-12 AWG Cable, 1/4″ Tab, Female
To connect to certain loads (i.e. 12V Sockets) , to make “removable” connections (i.e. Fridge, LEDs) and to connect cable of different gauge together (i.e. LED Dimmer) (25 Pack)
1 View
3 Heat Shrink Disconnect, 10-12 AWG Cable, 1/4″ Tab, Male 1 View
4 Heat Shrink Disconnect, 14-16 AWG Cable, 1/4″ Tab, Female 1 View
5 Heat Shrink Disconnect, 14-16 AWG Cable, 1/4″ Tab, Male 1 View
6 Heat Shrink Disconnect, 18-22 AWG Cable, 1/4″ Tab, Male 1 View
7 3M Scotchlok Quick Splice with Gel (14 AWG stranded) We used that to parallel our LED lights (25 Pack) 1 View
8 Heat Shrink Tubing Kit (with adhesive) To protect lug after crimping 1 View
9 Split Loom Tubing, 3/8″ diameter 25 feet To protect wire bundles 1 View
10 Split Loom Tubing, 1/2″ diameter 25 feet To protect wire bundles 1 View
11 Split Loom Tubing, 3/4″ diameter 10 feet To protect wire bundles 1 View
12 Nylon Cable Clamps Kit To secure cable/split-loom to wood 1 View
13 Zip Tie Mount with Adhesive To secure cable/split-loom to metal 1 View
14 Nylon Zip Ties Kit To secure cable/split-loom 1 View
15 Rubber Grommet Kit To protect wire from sharp edge (going through metal hole) 1 View
12V Loads

These are the appliances we personally use in our van:

# Item Quantity Buy Link More Info
1 Maxxair 6200K Roof Fan 1 Amazon Fan Installation
2 LED Ceiling Lights (Dimmable) 3 Amazon
3 PWM Dimmer for LED Lights, 12V, Slider 1 Amazon
4 Blue Sea 12V Socket 4 Amazon Electrical System Guide
5 Shurflo Revolution Water Pump, 3 GPM 1 Amazon
6 ON/OFF Switch for Water Pump 1 Amazon
7 Webasto Air Top 2000 STC Gasoline Heater 1 Amazon Webasto Installation
8 Propex HS2000 Propane Heater 1 Dealers Propex Installation
9 Novakool R5810 Fridge, 12V only 1 Campervan-HQ Fridge Guide
10 Sirocco ii Gimbal Fan, 12V 1 Amazon Sirocco ii Installation / Review
11 Nature’s Head Composting Toilet 1 Amazon Toilet Installation
12 Propane Solenoid Shutoff Valve 1 Amazon
13 ON/OFF Switch for Propane Solenoid 1 Amazon

These are essential to build your electrical system. Do NOT cheap out on tools (e.g. using pliers to crimp), or you'll compromise the performance and safety of your system.

#ItemDescriptionQTYView on Amazon
1Cable Cutter (up to 4/0 AWG)For large gauge cables1View
2Wire & Cable Cutter (2/0 – 22 AWG)Nothing to add!1View
3Wire & Cable Stripper (4/0 – 20 AWG)Nothing to add!1View
4Hydraulic Crimping Tool (4/0 – 10 AWG)Provides adequate, repeatable results for larger gauge lugs.1View
5Crimping Tool, Single-Crimp (8 – 22 AWG)Single-Crimp should be used with Heat Shrink connectors to prevent tearing the insulation and loosening the watertight connection (corrosion prevention)1View
6Heat Gun for Heat Shrink Connectors1800W, Variable Temperature Control1View
7Digital Multimeter (Voltage, Current, Continuity, Resistance)You don’t need it until you need it! Your friend when you need to troubleshoot…1View

Want More?


Stay in touch!


About us



Hello! We’re Isabelle and Antoine 🙂 In 2017, we sold our house (and everything in it), quit our engineering careers, and moved into our self-built campervan. Every day is an opportunity for a new adventure... We’re chasing our dreams, and hopefully it inspires others to do the same!

Heads Up: Exclusive Deals!

Thanks to all of you, we managed to negociate group discount on these. Strength in numbers!

142 thoughts on “Van Electrical Calculator”

  1. Hi guys – Thanks for the content! We bought your basic wiring diagram, and it (plus the items list and calculators) have been a huge help. Our loads and items list is very similar to yours, and includes one 120V AC wall outlet connected to the inverter buy a plug-in cord as recommended. There’s no “electrical box” behind the outlet though, and I was curious if you used one or not? They are plastic boxes that usually fit inside the wall behind an outlet when installed in a house. These aren’t recommended for any of the outlets, but just wanted to ask if an electrical box is needed behind the 120V outlet or 12V sockets? Thanks!

  2. What if I have more than 12 12 volt loads? Could I still make the one 12 load blue sea fuse block work?
    Thanks so much for your hard work building this site.

  3. Quick question – I’m thinking about buying access to your wiring diagram tool, but my battery is 24v and uses a voltage converter to step down for the 12v system. Will your tool be able to accommodate this?

  4. Hello Isabelle and Antoine,
    I feel dumb because I went through your pages and comments, somehow I didn’t find anyone with the same question: how do you get to use a fuse of175 amp for the 1000w inverter? I though I would just have to calculate W/v, so somewhere around 90amp.

    Thank you for your content, you are amazing. have a great day

    • You also have to account for efficiency, add a “buffer” and take into account temperature ampacity de-rating, so it’s more like W/V/efficiency x 1.4.
      But in the end we follow Samlex Owner’s Manual, it has the fuse size recommendation in it 🙂

  5. What a great site. I come here a lot and have shared it with others. It’s amazing what you’ve done. I’d like to send you some coffee to try. It’s super smooth dark roast. THANKS for all the guidance.

  6. Your Wiring Diagram – High Power is excellent! I couldn’t approach building out my van without it. Regarding the OEM cable for the heater, what is the size and length of that cable? And for all cables, I have assumed the length of the cable used to determine wire size is the physical length of the cable. But I have encountered installation manuals that use twice the length of the physical cable to account for the electrons traveling through the positive wire and back through the negative wire. The Espar M2 D4L Heater Manual is one example which uses twice the length of the physical cable resulting in a wire size of a whopping 6mm. Are there any component wires in your diagram that use twice the length of the physical cable to determine the wire size? Thanks.

    • The length used to calculate voltage drop is indeed always positive + negative (twice physical length). In the wiring diagram 12V DC load section you have to enter the one-way length because and the built-in calculator multiply the length by 2 (per tutorial page 8 bullet 3). In our wire gauge calculator you have to enter the return-length (positive + negative per note between “Wire Length” and input case). And then we also talk about that in our Electrical System Guide under section “7.1. Wire Diameter


  7. Thanks so much for everything you guys do for the community! My van wouldn’t be built without you! Quick question about the Victron solar chargers…the extra ground point on the side… did you do a second wire to the negative bus bar since the bus bar is grounded to the van as well?

    • It’s not mandatory to connect the ground point on the side in a mobile application, but it doesn’t hurt either to connect it to the negative bus bar!

  8. Thanks for your efforts, I would say that a very important addition to the resources you’ve provided is to discuss and recommend higher voltage battery banks.

    • It seems more and more people are leaning toward it. My understanding is that a higher voltage battery can provide the following benefits:
      – Use smaller cables (cost saving). Especially useful for system with inverter over 3000W (which requires massive cables).
      – Use twice the solar power for a given MPPT controller.
      – Slightly better conversion efficiency to 120V AC.

      Anything else I’m missing? Cheers!

  9. … U GUYS ROOOOOOOOOOOOCK !!!!!!!!!!!!!!!!


  10. Hi, thanks so much for publishing this calculator! We found it really useful when creating the electrical system for our van. We have now lived in the van for a few months and the electrical system is perfect for us!
    We have linked this post to our blog in the hopes that others find this useful tool too! Thanks for all the helpful info.

  11. I used your calculator to determine battery and inverter sizes. I’ve noticed that even if I only need the inverter for, say a low draw device like a laptop or TV, the calculator recommends a 1000 W inverter. Is there a reason for this? I think one can purchase a 700 W inverter from Renogy . Maybe they’re the only ones who make such a “small” inverter and since it’s in your budget category, it’s not factored into the calculator??

    • Even if you need less than 1000W inverter initially, I’d still recommend 1000W to make it “future proof”; chances are that you’ll need more than 700W eventually…

  12. Hello there! The calculator is recommending a 600 Ah Battery Bank for me, but the High Power Wiring Diagram will only let me select up to 4 batteries (I got 6 100Ah Lithium batteries). Do I need to make any changes, or just add in the extra 2?

  13. Thank you guys so much for all the information you provide. I am not looking to build out my van to the degree you have, but all the information and attention to detail is greatly appreciated. I bought a barebones Sprinter 4×4 new, already had a few issues with it. Luckily it was all fixed under warranty. But i think people like me love these Sprinters for the reason they’ve been making them for over 25 years. The ergonomics are incredible and it’s the most comfortable long distance vehicle I have owned. But like you state, dealerships are far in between and mechanics with the knowledge how to work on these vehicles are hard to come by. The Transit seems like a great alternative. Plus the back seats actually recline and fold away. Hopefully my van keeps going strong and I am looking forward to building it out a bit. It’s my daily driver but looking into a modular build so I can easily use it for the hauling and work I do, and adventures or living when possibly $h!+ hits the fan.
    I have forwarded your site to friends of mine. One who is looking to live in his van for a while and a few other van owners I know.
    Thank you again for this great detailed website. I know we all greatly appreciate the work you have done and shared with all of us.

  14. Hi hi!

    I just wanted to thank You both for provided as much detail as you do. It has made a tremendously large project more accessible for first timers. THANK YOU!

    I wanted to note that in my wiring diagram, the solar wire length does not sum in the field at the bottom for me. I had 15ft selected for both + & – and the sum does not reflect that. Forgive me if this is just something that I’m doing wrong and there is an easy answer.

  15. Hey you two,
    Alaskan here- I am building a van and use your site some or references on things I don’t do much (my solar is out of date, lithium batteries…), but a lot of it is boat similar, and there I am very current.
    So, if you need a warm dry place to do some repairs while in AK, I have a well tooled shop you can park in, gratis (for your great website).
    We are also Alaska wise, if we can help some with the lay of the land!

  16. Hey guys,

    Great resource. So much info on here. Thank you for all the time and work you put into the site.

    I pulled the trigger and purchased the diagram, and although it is nice being able to see the details up close, there are a few discrepancies that are making things complicated and seem conflicting. The diagram shows 2/0 wire for the main battery connections, while your shopping list shows 4/0. I was wondering if this was a dynamic field that might adjust with length, but it doesn’t appear to be. Would be great to update the diagram or the shopping list to be congruent.

    Also, many folks are using the Renogy RBC50D1S (DC-DC with MPPT, essentially charge controller and DC-DC in one box), and this has different wiring reqs and fusing requirements. I know it is hard to keep up with all the different and new technologies that are out there, and to build something that will work for many different systems, but I guess for $40, I was expecting a bit more from the diagram than what you already share for free on the site (which is a LOT!). Thanks!

    • Hi,
      The wire gauge size depends on the inverter you select (4/0 is for 3000W inverter); so if you select a different inverter in the calculator VS the wiring diagram, they won’t match.

      Everyone want to customize their system differently… It’s impossible for us to cover all the products and configurations imaginable. So we selected what we think it’s the best for most people (and for us).

      We know our diagram(s) are not perfect, but thanks for buying it anyway to support all the free stuff we have on our website.

    • The wire gauge you need varies with how much power you plan to pull, and the length of the run. When in doubt, go bigger. It’s more expensive, but you’ll lose less to resistance and if you upgrade in the future, your battery wires will already be nice and big.


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