Free calculators vs. the spreadsheet

The free tools on this site size one thing at a time. The paid spreadsheets run the same tested formulas for a whole build in one saved file (Excel, Google Sheets or LibreOffice, no macros). Here is exactly what each one does, checked against the files themselves.

Feature	Free site	12V Load & Wire Gauge spreadsheet	Overland Rig Planning Bundle (12V + Payload + Trip)
Wire gauge + fuse sizing	One circuit at a time	Up to 20 circuits side by side, each with a fuse check	Same (12V file included)
Load budget	Device list in the browser; not saved	25 device rows with presets, watts or amps, AC/DC, duty cycle	Same
Whole-system planning	Separate tools (some pass a number along by link)	System voltage set once on Start Here; Load Budget feeds Battery Sizing and Charging automatically	Same, plus a Start Here PDF that walks you through all three files in order
Inverter size with surge	✓ (free tool only)	Not included; inverter efficiency is applied to AC loads, and the inverter cable/fuse can be sized on Wire & Fuse	Not included (same as the 12V file)
Payload and gear list	One-screen payload check, lb only	—	150-row gear list with categories and locations; payload, GVWR, front/rear axle split from CAT-scale weights; roof load driving and parked; tent rating; tow, hitch and GCWR checks; heaviest 5 items; lb or kg
Trip planning	—	—	Up to 50 route legs, fuel range and jerry cans, water and food, trip budget and expenses, a 69-item starter packing list, and a budget-by-category chart
Your build saved	Nothing is saved (by design: no cookies, no accounts)	Your numbers stay in your own .xlsx file	Same, three files
Works offline	Needs the page open in a browser	Yes in Excel desktop or LibreOffice; also imports into Google Sheets	Same
Printing	Browser print of one result	Every tab set to print landscape, fit to page	Same
Fuse rules reference	Method notes on each page	Fuse Guide tab: placement, sizing limits, fuse families, DC breakers	Same
Price	Free	$9.00 on Etsy	$18.99 on Etsy

What's in the 12V spreadsheet (7 tabs)

Start Here: pick 12, 24 or 48 V, set inverter efficiency, step-by-step guide.
Load Budget: up to 25 devices (watts or amps, AC or DC, hours/day, duty cycle) → daily Ah and Wh.
Battery Sizing: LiFePO4 and AGM side by side (usable depth of discharge, days of autonomy, margin).
Charging: solar plus DC-DC plus shore power against daily use, surplus or deficit, days until empty.
Wire & Fuse: up to 20 circuits; smallest copper AWG meeting voltage drop (ABYC, 3%/10%) and ampacity, NEC cross-check, suggested fuse, and a check-a-wire box.
Fuse Guide and Tables with sources listed.

What the bundle adds

Overland Payload, Roof Load & Towing Calculator: Rig Setup, a 150-row Gear List, and a Load Check of payload, GVWR, axles, roof (driving and parked), tent and towing.
Overland Trip Planner: Trip Setup, Route Legs, Trip Summary, Expenses and a Packing List.
A one-page Start Here PDF. The three files are separate (no links between files); the PDF shows which numbers to carry from one to the next.

Prefer free? Every single calculation is here one at a time: wire gauge, fuse, battery, charging, inverter, payload, plus the free printable cheat sheet.

Safety: this is a planning estimate, not an engineering sign-off. DC systems can start fires and lithium batteries can deliver very high fault current. Check every result against the manufacturer's instructions and current ABYC/NEC or local rules, put a correctly rated fuse or breaker close to the battery on every positive cable, and have a qualified installer check work you are not sure about. We are not responsible for how results are used.

Planning a whole build?

The paid spreadsheets run these same tested formulas for a whole build in one saved file. Compare free vs. spreadsheet.

Overland Rig Planning Bundle (12V + Payload + Trip spreadsheets) on Etsy, $18.99

12V Load & Wire Gauge Calculator spreadsheet on Etsy, $9.00