Ten free calculators for sizing solar and off-grid power systems — from a single panel estimate to a complete vanlife, RV, or cabin build. Each tool uses the same public formulas installers use, shows its working, and runs entirely in your browser: no signup, no email, nothing sent to a server.
How to size an off-grid system, in order
Component sizes depend on each other, so the order matters. Loads come first; everything downstream is sized from them.
Total your daily load. List everything you’ll run, with watts and hours per day, to get daily watt-hours. The Battery Runtime Calculator shows how long any candidate battery carries that load, and the Wh ↔ Ah Converter translates between the units battery spec sheets mix freely.
Size the battery bank. From daily watt-hours, days of autonomy (cloudy days you want to ride out), and a safe depth of discharge for your chemistry, the Battery Capacity Calculator gives the bank size in Ah and kWh.
Size the panel array. The Off-Grid Solar Calculator turns daily load, your location’s peak sun hours, and system losses into array watts and a panel count. Use the Panel Angle & Tilt Calculator to get the most out of those panels at your latitude.
Size the inverter. The Inverter Size Calculator takes your appliance list and returns the continuous and surge watts the inverter must handle. The Watts to Amps Calculator converts those watts into the currents your fusing and wiring see.
Size the wiring. Last, because it needs the currents and distances everything above produced: the Solar Wire & Cable Size Calculator picks a gauge from current, run length, and the voltage drop you’re willing to accept.
Loads → battery bank → panel array → charge controller → inverter → wiring. Every component downstream of your daily watt-hours is sized from them, so totalling loads honestly (including winter usage) is the step that decides whether the whole system works. The workflow above walks the chain tool by tool.
Do these work for an RV, van, or boat system?
Yes — the math is identical whether the system sits on a roof rack or a cabin. The differences are practical: mobile systems usually run 12 V or 24 V, see more shading and panel-angle compromise, and have hard limits on battery weight and roof area. Enter your real numbers and the calculators handle the rest.
Are the results safe to wire from directly?
They’re sizing estimates from public formulas, with every assumption shown — a solid planning baseline, not an electrical design service. For a permanent installation, confirm conductor sizes and overcurrent protection against your equipment ratings and local code, and have the work checked by a qualified electrician.
Do the calculators store or send my numbers?
No. Every tool on this site runs as JavaScript in your browser. Your inputs never leave your device — there’s no account, no server-side calculation, and nothing to delete afterwards.