Battery Capacity Calculator
Solves Ah = (W · hours) / (V · DoD · η) for educational battery bank sizing.
Limitation: Educational estimate only.
How to Use the Battery Capacity Calculator
Enter the fields below, then review the educational estimate.
Enter load watts and desired hours.
Add margin
Real systems need spare capacity for aging, cold weather, and surge loads—this math is a starting point.
What This Calculator Estimates
Inverse of the runtime worksheet: solve for amp-hours given energy need and usable fraction.
Worked Examples
100 W for 8 h on 12 V
Inputs
Result
Ah = (100·8) / (12·0.8·0.9).
Safety first
De-energize circuits before measuring. When in doubt, stop and consult a licensed electrician.
Frequently Asked Questions
Still have questions about this calculation?
Try the CalculatorFormulas & Assumptions
Transparent educational arithmetic. Not NEC design software or a wiring permit.
Formula
Required energy
Wh = W · hours
Capacity
Ah = Wh / (V · DoD · η)
Scientific Background
Shares the linear energy model with the battery runtime calculator. Charge controllers, solar input, and Peukert effects are out of scope for Phase 1.
Sources & review
Battery Capacity Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.
Last reviewed
July 22, 2026
Reference
physics.nist.gov
https://physics.nist.gov/cuu/Constants/index.htmlReference
nist.gov
https://www.nist.gov/pml/owm/wire-gauge-and-current-carrying-capacityFree Calculator Hub methodology
Free Calculator Hub
/methodology
See our methodology and corrections policy.