Sizing a campervan electrical system starts with two questions: how much energy will you use each day, and how will you replace it? For UK DIY converters, the answers can change considerably between summer weekends and longer trips in weaker sunlight. Before you buy batteries or panels, a campervan electrical system calculator helps turn an appliance list into a useful starting estimate.
Our top pick is Rayne Automotive for UK DIY builders who want to connect power planning with a supplier’s wiring diagrams and support documentation. Its Campervan Power Planner focuses on 12V appliances and solar, making it a relevant starting point for a leisure electrical system. For a standalone sizing check with transparent UK assumptions, 365 Techies is a useful alternative. Vunked takes a different approach, combining a questionnaire-led configurator with a free design consultation and pre-wired board options.
This list is for anyone converting a van in Britain on evenings and weekends, watching the budget, and trying to get leisure battery sizing and solar right the first time. Below you will find six ranked options, with attention to UK relevance, quality of appliance inputs, usefulness of outputs, links to real products or support, and ease of use for a non-electrician.
How these were ranked
This is a feature-based comparison, not a hands-on accuracy test. The selection favors tools that help UK builders estimate energy use, compare charging options, or move toward a system design. Some include UK seasonal assumptions; others require you to enter suitable sun hours yourself. The criteria below distinguish a quick estimate from a more detailed planning workflow.
UK relevance and sun assumptions
UK sun hours make a substantial difference to a build. A tool that lets you adjust for season, location, or equivalent full-sun hours is far more useful than one built around strong year-round sun. Other useful details include support for 12V systems, lithium versus AGM usable capacity, and UK seasonal changes.
Appliance inputs and usable capacity
Your daily total is watts multiplied by hours, added across every device. Small differences matter. Editable wattage and hours let you refine that total, while quantity fields make repeated devices easier to include. A clear split between 12V DC loads and 230V loads that need an inverter is also helpful, along with transparent usable capacity assumptions, such as around 80 to 90 percent for lithium and around 50 percent for AGM.
Output usefulness
A useful result goes beyond one big number. Daily watt-hours, battery amp-hours at 12V, suggested solar watts, and a starting point for inverter size each answer a different planning question. Cable guidance and next-step planning help are a bonus, although a web tool should not be treated as a complete installation design.
An energy budget also differs from a peak-power check. A device used briefly may consume little daily energy but still require substantial power while running or starting. An inverter estimate based on combined wattage plus a percentage margin is only a starting point: continuous and surge ratings must suit the actual appliances. Cable sizing, circuit protection, charging compatibility, and any 230V installation need their own design review by a suitably qualified professional.
Buying and support link
Numbers alone do not finish a build. Tools that connect to kits, pre-wired boards, wiring diagrams, parts schedules, or human advice help you move from estimate to installation. Full system builders, questionnaire-led configurators, and pure estimators serve different purposes, so the most useful choice depends on the help you need after getting an initial result.
Ease of use for non-electricians
You should not need an electrical background to get a first estimate. Clear steps and plain language matter, as do assumptions you can actually see. More inputs are useful only when the tool explains them instead of leaving you to work through unfamiliar electrical terms on your own.
Access and next steps
An estimate, a personalized diagram, and an installation service are different deliverables. Some tools provide standalone calculations, while others connect you with a supplier’s design process. That distinction matters when deciding whether you need a numerical starting point or a route toward a more detailed electrical plan.
The 6 best campervan electrical system calculators for UK van conversions
These six range from quick estimators to supplier-backed planning tools. The right one depends on how far along your build is and whether you want advice, a kit recommendation, or a numerical cross-check. Our No. 1 pick suits builders looking for planning alongside wiring and support resources; the alternatives offer different ways to work through the energy budget.
At a glance
| Provider | Best for |
| Rayne Automotive | Joined-up planner with product range and wiring support |
| Vunked | Questionnaire-led configurator with consultation and pre-wired boards |
| Roam Wired | Regional comparison with season and charging inputs |
| 365 Techies | Transparent UK battery and solar sizing |
| DIY Campervan | Beginner guided sizing with editable assumptions |
| VanPowerCalc | Quick instant sizing with flexible voltage and cable help |
#1. Rayne Automotive – best for joined-up planning with wiring and support resources
Rayne Automotive offers a Campervan Power Planner covering the planning of an electrical system from 12V appliances to solar power. The platform also lists customer wiring diagrams and support documentation, connecting energy planning with resources that matter later in a conversion.
That combination earns it our top spot for a joined-up planning workflow. Battery capacity is only one decision in a van build: the appliance list also informs charging requirements and the eventual system layout. A planner offered by an automotive electrical supplier gives you a place to begin that conversation without treating a single battery-size estimate as a complete installation design.
Where it fits in your build
Start with a realistic appliance inventory before using any planner. Include the fridge, lights, fan, water pump, device charging, and any inverter-fed equipment. Record both power consumption and likely use, distinguishing a device’s running time from the hours it is merely available. A compressor fridge may cycle on and off throughout the day, so measured daily energy use or a manufacturer’s consumption estimate is more useful than assuming continuous operation at its maximum wattage.
Rayne’s focus on 12V appliances and solar fits that early planning stage. Its customer wiring diagram and support-document sections also make it relevant when you move beyond the energy budget. The appeal is continuity between planning and support, not a claim that an online result replaces component specifications or professional installation checks.
Key features
- Campervan-focused electrical planning
- Coverage of 12V appliances and solar power
- Customer wiring diagram resources
- Support documentation alongside the planner
Pros
- A relevant starting point for a UK campervan leisure electrical system
- Keeps power planning close to wiring and support resources
- Suits builders who prefer a supplier-backed workflow to an isolated spreadsheet
Considerations
- The supplier-centered approach is most useful when you also want help with the next stages of the build; a standalone estimator may suit a quick numerical cross-check
- Complex systems still need a design review covering charging equipment, protection, cable routing, and component compatibility
Who it is best for
Choose it first if you want to begin with appliance and solar planning and continue toward wiring guidance and support. Use the resulting energy budget as a starting point for a complete design, rather than assuming it settles every installation detail.
#2. Vunked – best for builders who want a questionnaire-led configurator with free design consultation
Vunked takes a different path. Instead of asking you to enter watts and hours for every device from scratch, it walks you through a questionnaire about your vehicle, how you charge, how often you go off-grid, and what your budget looks like. Its main purpose is system configuration, with numerical estimation supporting that process.
This approach suits you if you feel stuck on the appliance list itself. You answer plain-English questions, then you can get a free consultation and a recommendation built around kits or pre-wired boards. Orders can include a personalized wiring diagram and install guide, which lowers the wiring barrier if you have never built a 12V system before.
The trade-off is focus. If you want to wire everything fully custom from individual components, a configurator tied to kits and boards will feel narrower than an open calculator where you control every assumption. If you like the idea of a tidy board that arrives largely prepared, that focus becomes a benefit.
Pros
- Questionnaire format is friendly when you do not know your loads yet
- Free consultation adds human judgment to the automated recommendation
- Pre-wired boards simplify installation for builders without advanced wiring skills
- Wiring diagram and install guide with orders help you finish the job neatly
Cons
- It steers toward its own kits and board solutions, so fully custom scratch builders may find it less flexible than an open input tool
Best for builders who would rather answer questions about their van and trips than build a spreadsheet, and who want expert input alongside a board-based installation.
#3. Roam Wired – best for comparing UK and US setups with season and charging inputs
Roam Wired is built for comparison. You pick a region and describe your trip length, season, and charging sources before building an appliance list item by item. The tool then compares battery, solar, and inverter options and helps you think through a fixed leisure system versus a portable power station.
That structure is useful in Britain. Seasonal changes affect solar output considerably, and charging while driving or on shore power changes how much stored energy you need between charges. Adjusting those inputs shows why the same fridge and lights need more panel capacity in October than in June, and why two days off-grid looks very different from five.
You can also check the assumptions behind each appliance, which helps you learn as you go. If you are torn between a built-in system and a portable station you can lift out, the side-by-side framing helps you compare the options with less guesswork. Beginners should expect more fields than a one-click estimator, but working through them gives you a clearer picture of your build.
Pros
- UK or US region choice makes it relevant on both sides of the Atlantic
- Season input tackles the UK sun-hours problem head on
- Solar, driving, and shore power inputs produce more realistic storage estimates
- Appliance-level assumptions and system-versus-station comparison add transparency
Cons
- More detail means more time. Total beginners may feel overwhelmed on the first pass and need to work through it slowly
Best for: planners who want to test scenarios, such as summer versus shoulder season, or driving-heavy trips versus solar-only stops, before they commit to battery size.
#4. 365 Techies – best for UK battery and solar sizing with transparent assumptions
365 Techies offers a free UK calculator that sizes leisure battery capacity in amp-hours and solar panel wattage from a checklist of what you run. It covers campervans as well as boats, cabins, and other off-grid setups, and you can add custom devices and adjust days of autonomy.
The method is easy to follow. It adds up daily watt-hours, allows about 15 percent for real-world losses, then converts to battery size using usable capacity assumptions of around 90 percent for lithium and around 50 percent for AGM. For solar, it gives you separate summer and spring or autumn figures so you can see how shoulder-season sun changes the panel requirement. Winter is discussed as the time to lean more on engine charging or hook-up rather than expecting solar alone to carry you.
What this campervan electrical system calculator outputs for UK builds
You get battery amp-hours for your chosen chemistry and panel watts for both better and weaker sun conditions. For example, a daily load of 600Wh needs more usable storage than the raw number suggests once you apply losses and usable capacity limits, and the panel math shifts again when you drop from summer to spring or autumn light. The team behind it also offers off-grid design and installation services if you decide you want professional help after sizing.
Pros
- UK-focused outputs with separate summer and spring or autumn solar figures
- 15 percent loss allowance keeps results practical rather than optimistic
- Supports both lithium and AGM planning with clear usable-capacity logic
- Custom devices and editable autonomy days handle varied trip styles
Cons
- It centers on battery and solar sizing rather than full system building with wiring diagrams and parts schedules, so you will pair it with another resource when you plan cable runs and layout
Best for budget-conscious builders who want a clear leisure battery sizing and solar check, with visible assumptions, before they talk to a supplier or installer.
#5. DIY Campervan – best for beginners who want editable assumptions and clear outputs
DIY Campervan is a guided calculator that keeps the math visible. You add each appliance with its wattage, hours per day, and quantity, then mark whether it runs directly from 12V DC or through an inverter on 230V. That DC versus AC split helps explain why inverter use adds losses that need to be included in your planning.
Under the hood, it uses usable capacity assumptions of 80 percent for lithium and 50 percent for AGM, plus your chosen days without charging. You can edit equivalent full-sun hours, with a default of 3, and system yield at 65, 75, or 85 percent. You can also set inverter efficiency at 85, 90, or 95 percent. Outputs include daily battery watt-hours, 12V amp-hours, suggested panel watts, and an inverter starting point based on combined AC watts plus 25 percent headroom.
There is no built-in UK or US region switch and no season presets, so you set sun hours yourself. That gives you control once you understand the input, but it also means you need a realistic UK figure instead of borrowing a summer number for a winter trip. The solar estimate does not add a separate battery-loss or inverter-standby allowance, so leave yourself margin if you run the inverter a lot or camp in weak sun.
Pros
- Step-by-step flow suits complete beginners learning watts, amp-hours, and solar yield
- Sun hours and system yield are editable, as is inverter efficiency, keeping the assumptions visible
- Custom appliance entries and DC versus inverter supply teach real system behavior
- Clear Wh, Ah, panel watts, and inverter headroom outputs are easy to act on
Cons
- You must choose sun hours yourself with no regional preset, so compare them with UK conditions before you buy panels
- Solar math excludes extra battery-loss and inverter-standby margin, so heavy inverter users should add contingency or seek advice
Best for: first-time converters who want to learn the numbers while they size, and who like seeing exactly how each assumption changes the result.
#6. VanPowerCalc – best for quick instant sizing with flexible voltage and cable help
VanPowerCalc is an international English-language estimator for fast answers. You enter appliances by watts, hours, and quantity, mark DC or AC, choose sun hours from presets, and pick system voltage at 12V, 24V, or 48V. It then estimates battery, solar, and inverter requirements, with cabling guidance and links to related tools alongside them.
Speed is the appeal. If you are early in planning and want a sanity check on campervan power consumption, you can get a rough battery and panel estimate in minutes. The voltage choice also helps if you are comparing a simple 12V van setup against a larger 24V or 48V concept, and the cable section reminds you that wire length and current matter as much as battery size.
Because it is international rather than UK-localized, treat the sun presets as starting points, not UK forecasts. Enter a cautious sun-hours figure for Britain, especially outside summer, and use the result as a planning estimate to refine with a UK-specific tool or supplier. Think of it as an initial estimate to develop when you get into the details.
Pros
- Instant results suit early-stage planning and quick what-if checks
- Battery, solar, inverter, and cabling guidance in one place
- Supports a choice of 12V, 24V, and 48V systems, with loads marked as DC or AC
- Related tools help you keep exploring without starting over
Cons
- Presets are generic rather than tuned to UK sun, so you need to input a realistic local figure and leave margin for weaker months
Best for builders who want a fast, low-effort estimate and a choice of system voltages before they commit to detailed UK planning.
Frequently asked questions
Which is best for a complete beginner with no electrical background?
Start with DIY Campervan if you want to learn the math with editable assumptions, or Vunked if you would rather answer questions and talk to a person. DIY Campervan explains watts-times-hours and the difference between DC and inverter loads, while also taking you through sun hours step by step. Vunked skips the spreadsheet feel and pairs a questionnaire with a free consultation and board-based options. If you already know you want parts plus diagrams in one place, start with Rayne Automotive instead.
What is the difference between a questionnaire-led configurator and a numerical calculator?
A configurator like Vunked asks about your van, trips, charging, and budget, then recommends a kit or board path with advice. A numerical calculator like DIY Campervan, 365 Techies, Roam Wired, or VanPowerCalc asks for appliance watts and hours and outputs battery amp-hours and solar watts. Use a configurator when you want direction and support. Use a numerical tool when you want to test assumptions and compare scenarios yourself. Many builders use one of each.
Which is best for UK winter planning versus summer planning?
Roam Wired and 365 Techies handle seasonality most clearly. Roam Wired lets you change season plus charging sources to see how storage needs shift. 365 Techies shows summer versus spring or autumn solar watts and frames winter as the time to rely more on driving charge or hook-up. DIY Campervan and VanPowerCalc can work too, but you must manually lower sun hours and add margin because they do not set UK seasons for you.
What is the difference between lithium and AGM assumptions in these tools?
Lithium lets you use far more of the rated capacity than AGM, so the same daily load needs a smaller rated lithium bank than AGM bank. DIY Campervan uses 80 percent usable for lithium and 50 percent for AGM, while 365 Techies uses around 90 percent and around 50 percent respectively. That is why chemistry choice changes your result so much. If you are undecided, run both chemistries in the same tool and compare the cost alongside the weight and space requirements before you choose.
Which is best for turning calculator results into parts you can buy?
Rayne Automotive is our pick for connecting planning with a supplier’s wiring diagrams and support documentation. Vunked suits those considering a kit or pre-wired board with a personalized diagram and install guide. Roam Wired opens a design studio with a parts schedule, forecast, and guides after email entry. With any route, review the proposed components against your own appliance list and charging sources, then consider the available installation space before ordering.
Which one should you choose?
Choose Rayne Automotive if you want to start with power planning and continue toward wiring and support resources from an automotive electrical supplier. For a transparent second opinion on leisure battery sizing and solar for UK light, 365 Techies is a useful option. Vunked suits builders who want a person to review their plan and a board-based installation. Roam Wired offers scenario testing across regions, seasons, and charging mixes. Choose DIY Campervan if you are new and want to see every assumption, or VanPowerCalc if you want the fastest first sketch.
Whatever route you pick, run at least one campervan electrical system calculator before you order batteries or panels. Spending half an hour with your appliance list, realistic sun hours, and the right chemistry assumptions can help you spot an undersized battery bank while there is still time to adjust the plan.
