The Locolory toolkit / Electrical & Off-Grid
Solar & Battery Bank Sizing Calculator
Calculate total daily watt-hour consumption, size deep-cycle Lithium or AGM battery banks, and determine required inverter and AWG wire gauges.
Solar & Battery Bank Sizing Calculator is a free browser-based utility that calculate total daily watt-hour consumption, size deep-cycle Lithium or AGM battery banks, and determine required inverter and AWG wire gauges.
- Core logic: sum appliance watt-hours, then apply system voltage, usable depth of discharge, losses, and peak load sizing.
No software download, login, or server upload required. Computations execute locally on device.
Off-grid energy ledger
● Calculated locally
Example appliance ledger
Daily loads
Replace the example rows with measured appliance consumption.
Daily energy540 Wh
Daily energy100 Wh
Daily energy260 Wh
Use the inverter datasheet value; 85% is a conservative default.
System capacity
90% usable battery capacityRecommended minimum battery bank197 Ah @ 12V
2353 Wh nominal storage for 2 days
Watt-Hours vs Amp-Hours: How to properly calculate battery bank capacity
Energy is voltage multiplied by charge: Wh = Ah × V. The same 1,200 Wh is 100 Ah at 12 V, 50 Ah at 24 V, or 25 Ah at 48 V, so an Ah rating is meaningful only with its nominal voltage.
Battery capacity must also cover inverter loss, cloudy-day autonomy, and usable depth of discharge. This estimator divides required load energy by efficiency and usable DoD rather than treating the nameplate bank as fully available.
Cable and inverter planning assumptions
The inverter result adds 25% to the sum of listed wattages and assumes all loads may run together. Motor, compressor, and power-supply startup surge can require a substantially larger surge-rated inverter.
The cable result assumes copper, a 3% maximum voltage drop, and the selected one-way distance. Cable routing, insulation, terminals, ambient temperature, conduit, and fuse coordination may require a larger conductor.
Copper conductor reference
DC Wire Gauge (AWG) Amperage and Voltage Drop Table
Example minimums for a 30A load, 3% voltage drop, and the listed one-way cable run. Verify ampacity and code.
| System voltage | One-way run | Calculated copper minimum | Round-trip circuit |
|---|---|---|---|
| 12V | 5 ft | 8 AWG | 10 ft |
| 12V | 10 ft | 6 AWG | 20 ft |
| 12V | 20 ft | 4 AWG | 40 ft |
| 24V | 5 ft | 8 AWG | 10 ft |
| 24V | 10 ft | 8 AWG | 20 ft |
| 24V | 20 ft | 6 AWG | 40 ft |
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Good questions. Clear answers.
How do I convert watt-hours (Wh) to amp-hours (Ah)?
Divide watt-hours by nominal system voltage: Ah = Wh ÷ V. For example, 1,200 Wh is 100 Ah at 12 V but 50 Ah at 24 V. Add conversion losses and usable depth of discharge when sizing the actual bank.
Why can you use 90% of a lithium battery but only 50% of an AGM battery?
LiFePO4 chemistry and its battery-management system generally tolerate deeper regular cycling with less life penalty. Repeated deep discharge accelerates sulfation and capacity loss in lead-acid batteries, so 50% usable depth is a common planning limit. Follow the battery manufacturer's cycle-life data.
What size battery bank do I need to run a 12V RV refrigerator?
Multiply its measured average watts by daily run time, then allow for autonomy, conversion loss, and battery depth of discharge. A compressor refrigerator's label wattage is not its 24-hour average because it cycles; a plug-in energy meter gives a better daily figure.
How do I determine what size DC wire gauge to run from my battery to inverter?
Use the inverter's maximum DC current, cable round-trip length, allowable voltage drop, conductor material, insulation rating, bundling, temperature, and protection device. This tool checks copper cable against 3% voltage drop and a conservative current allowance, but final cable and fuse sizing must follow equipment instructions and applicable code.