Ampere to Amp-Hour Calculator

Calculate required battery capacity (Ah), estimated runtime, or maximum continuous current. This tool goes beyond basic multiplication by modeling real-world inverter losses and Depth of Discharge (DoD) constraints for modern energy systems.

1. Calculation Target

What are you solving for?

2. Electrical Variables

Continuous Current Draw Amps (A)

Operation Time Hours

3. Chemistry & System Efficiency

Battery Chemistry (DoD Limit)

Discharging lead-acid past 50% permanently damages the cells. LiFePO4 can safely cycle to 80-90%.

System Inefficiency & Inverter Loss %

DC to AC inverters typically waste 10-15% of energy as heat.

Calculation Results

Required Battery Capacity

— Ah

The actual nameplate battery size you need to purchase.

Battery Capacity Allocation

Understanding real-world battery sizing

The "Usable Capacity" Illusion

A common mistake in solar and off-grid builds is assuming a 100Ah battery provides 100Ah of power. Depth of Discharge (DoD) determines how much energy you can extract before permanently damaging the cells. Traditional Lead-Acid and AGM batteries are strictly limited to 50% DoD. If you need 100Ah of usable power, you must buy a 200Ah lead-acid battery.

The 2026 Lithium Standard

Lithium Iron Phosphate (LiFePO4) chemistries safely discharge to 80% or 90% DoD without degradation, providing 4,000 to 6,000 cycles. While a LiFePO4 battery costs more upfront, a single 100Ah lithium battery delivers the exact same usable energy as a heavy, bulky 160Ah lead-acid bank.

Account for Inverter Inefficiency

If your battery (DC) is powering household wall outlets (AC), the power must run through an inverter. The conversion process generates heat, typically wasting 10% to 15% of your total battery capacity. You must upsize your battery bank to compensate for these parasitic losses.

Beware Peukert's Law (Lead-Acid Only)

Lead-acid capacities are rated on a 20-hour slow discharge curve. If you pull a massive amount of current out of a lead-acid battery quickly (e.g., running a microwave in 1 hour), the total capacity of the battery shrinks exponentially due to internal resistance. Lithium batteries are almost completely immune to Peukert's Law and deliver full capacity regardless of how fast you drain them.

2026 Battery Chemistry Breakdown

Chemistry Type	Safe Depth of Discharge (DoD)	Expected Cycle Life	Peukert Effect / Fast Drain Loss
Flooded Lead-Acid	50%	300 – 500 Cycles	Severe (Up to 40% loss at 1hr rate)
AGM / Gel (VRLA)	50%	400 – 800 Cycles	High (Up to 30% loss at 1hr rate)
Lithium Ion (NMC)	80%	1,000 – 2,000 Cycles	Minimal
Lithium Iron Phosphate (LiFePO4)	80% – 90%	4,000 – 6,000+ Cycles	Negligible (Near 100% efficiency)

Frequently asked questions

What is an Amp-Hour (Ah)?

An Ampere-Hour is a unit of electrical charge capacity. It means a battery can theoretically deliver 1 amp of current for 1 hour. A 100Ah battery could theoretically deliver 1 amp for 100 hours, or 10 amps for 10 hours. However, real-world chemical limits prevent 100% extraction.

Does voltage matter for Amp-Hours?

Yes. Amp-hours only measure capacity, not total energy. A 12V 100Ah battery holds 1,200 Watt-Hours of energy (12 * 100). A 48V 100Ah battery holds 4,800 Watt-Hours. When calculating loads, ensure your amp draw is measured at the same voltage as your battery bank. If you are powering a 120V AC microwave from a 12V DC battery, the inverter pulls 10 times the amps from the battery to step up the voltage.

Why are LiFePO4 batteries better in 2026?

LiFePO4 (Lithium Iron Phosphate) has fully dominated the energy storage market because it is inherently non-combustible (unlike NMC lithium-ion), lasts over 10 years even with daily cycling, and provides 80% usable capacity without the voltage sag experienced by aging lead-acid banks.

About this calculator

This calculator resolves standard electrical capacity equations (I × T = C) while enforcing critical real-world de-rating factors like DoD and thermodynamic inversion losses.

The mathematical engine utilizes the following field logic:

Battery Sizing (Finding Ah):
Consumed Energy = Amps × Hours
Required Usable Energy = Consumed Energy ÷ (1 − System Loss %)
Nameplate Battery Size = Required Usable Energy ÷ DoD Limit

Runtime (Finding Hours):
Gross Usable Energy = Nameplate Ah × DoD Limit
Net Usable Energy = Gross Usable Energy × (1 − System Loss %)
Estimated Runtime = Net Usable Energy ÷ Amps

Max Current (Finding Amps):
Gross Usable Energy = Nameplate Ah × DoD Limit
Net Usable Energy = Gross Usable Energy × (1 − System Loss %)
Max Continuous Draw = Net Usable Energy ÷ Hours

Methodology and sources

Ampere to Amp-Hour Calculator applies the engineering relationship and unit conversions described on this page to the inputs entered above. The result is an estimating and checking aid. Final equipment selection or installation should also be verified against manufacturer data, current local codes and a qualified professional where required.

Source note: This calculator is driven by standard arithmetic and the values supplied by the user. No unrelated third-party source has been added merely for authority; any benchmark assumptions used by the tool are stated in its About section.

Last reviewed: August 2026. The linked organizations provide reference material and do not endorse Efficienco or this calculator.