Free Power System Tools

Quick, standards-based calculators for boat, RV, and off-grid electrical system design. No signup required.

Battery Sizing Calculator

Size a battery bank by chemistry (LiFePO4, AGM, Gel, Flooded), daily load, and days of autonomy. Depth-of-discharge aware.

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Solar Sizing Calculator

Panel count, charge controller amps, and MPPT-vs-PWM recommendation from your daily Wh and local peak sun hours.

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Inverter Sizing Calculator

Off-grid / mobile inverter sizing with diversity factor and 3× motor starting surge. Accounts for induction motors (pumps, compressors).

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ABYC E-11 Wire Gauge Calculator

Wire AWG recommendation with voltage drop and fuse sizing per ABYC E-11 — the standard marine surveyors reference.

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Want a full system design?

Combine loads, batteries, solar, and wire into a professional PDF report with PowerLab Pro.

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What these tools are, and are not

These calculators produce design documentation to check your own work against — not a stamped plan set, and not a substitute for the published standard. Nothing here carries a Professional Engineer or P.Eng seal, and no output is reviewed by a licensed engineer before you see it.

Values are cited to section numbers only; we do not reproduce code text. Requirements differ by edition and by jurisdiction, and the authority having jurisdiction may interpret or amend them. Acceptance is never guaranteed. The licensed person who signs and submits the work remains responsible for verifying every number against the current adopted code.

Marine (ABYC E-11) outputs are DRAFT: those tables are transcribed from published reproductions and are pending sign-off by a licensed marine electrician. Verify any final installation with a qualified professional.