Free tool
Amp Hours to Watt Hours Calculator
Watt-hours are amp-hours times voltage. A 100 Ah label means nothing for energy until you know whether the pack is 12 V or 48 V.
Wh = Ah × volts
Wh = Ah × V. 100 Ah at 48 V is 4,800 Wh (4.8 kWh); at 12 V the same Ah rating is only 1.2 kWh. Apply depth of discharge for usable DC energy, and inverter efficiency if you need the figure at the AC terminals.
The inverse is watt-hours to amp-hours. For runtime from a wattage, use watts to kWh.
The capacity
Nameplate amp-hours of the pack or bank.
Nominal pack voltage — required. Ah alone never give Wh.
Fraction of nameplate you actually plan to use. 100% makes usable equal nameplate.
The answer
Nameplate energy
4,800.00 Wh
(4.80 kWh)
Wh = Ah × V → 100.00 × 48.00
Usable at 80% DoD (DC)
3,840.00 Wh
3.84 kWh — nameplate × DoD.
Usable at the AC terminals (90% inverter)
3,456.00 Wh
3.46 kWh. That is the AC load energy the pack can support under these assumptions — not a runtime by itself, which also needs the load's watts.
What this does not tell you
How many hours a load will run — divide usable Wh by the load's watts (see the watts to kWh calculator). Surge / starting headroom. Whether the pack is legal to install where you want it.
Informational use only, please verify before you rely on it
This reproduces the standard relationship Wh = Ah × V, with optional depth-of-discharge and inverter-efficiency adjustments. It is a preparation aid, not a determination. It does not size conductors, overcurrent protection or inverters, and it does not decide whether a battery may be installed in a given location. Confirm against the equipment nameplates and applicable codes.
This tool is provided for general informational and educational purposes only. Its output is an illustrative estimate generated from the values you enter and from general assumptions that will not match every deal, market, lender, or homeowner. It is not tax, legal, accounting, financial, or professional advice, and it is not a quote, an offer, a credit decision, or a guarantee of pricing, approval, timing, savings, or eligibility.
You are solely responsible for independently confirming all information presented here including any figures, rates, fees, margins, timelines, tax treatment, and federal, state, local, or utility incentives, with the applicable lender, authority having jurisdiction, and your own qualified tax, legal, and financial advisors before acting on it, relying on it, or presenting it to a homeowner or any third party. Incentive programs, lender terms, and permitting requirements change frequently and vary by jurisdiction.
Seamless Home is not a tax advisor, law firm, lender, or licensed installing contractor, and makes no representation or warranty as to the accuracy, completeness, or currency of the information produced by this tool. To the fullest extent permitted by law, Seamless Home accepts no liability for any decision made or action taken in reliance on it.
Nameplate Ah is not runtime
Converting to watt-hours tells you how much energy the pack stores under the assumptions you entered. Hours of backup still require dividing by the load's watts — and starting surges are a separate inverter limit. The battery siting checker and where a home battery can and cannot be installed cover the location rules that sit beside the math.
Frequently Asked Questions
How do you convert amp-hours to watt-hours?+
Multiply amp-hours by the battery voltage: Wh = Ah × V. 100 Ah at 48 V is 4,800 Wh, or 4.8 kWh. Amp-hours alone never convert — without a voltage there is no watt-hour figure.
How many watt-hours is a 100 Ah battery?+
It depends on the voltage. At 12 V, 100 Ah is 1,200 Wh (1.2 kWh). At 24 V it is 2,400 Wh. At 48 V it is 4,800 Wh. Always state the voltage with the Ah figure.
What is usable capacity?+
The fraction of nameplate energy you plan to draw. At 80% depth of discharge, a 4,800 Wh nameplate yields 3,840 Wh of usable DC energy. Manufacturers set different limits for lead-acid and lithium chemistries — use theirs.
How do I estimate AC load support?+
Multiply usable DC watt-hours by the inverter efficiency. 3,840 Wh through a 90% inverter is about 3,456 Wh at the AC terminals. Runtime is that figure divided by the load's watts.
Why do two 100 Ah batteries have different Wh?+
Because they are at different voltages, or because one figure is nameplate and the other is already derated for depth of discharge. Convert both to watt-hours at a stated voltage before comparing them.
How do I go the other way?+
Divide watt-hours by voltage: Ah = Wh ÷ V. The watt-hours to amp-hours calculator does that and can size the pack for a stated depth of discharge.
Is this a determination?+
No. It reproduces the standard relationship Wh = Ah × V as a preparation aid. It does not size an inverter or the wiring, does not calculate runtime by itself, and does not decide whether a battery may be installed where you want it.
Related resources
Watt Hours to Amp Hours Calculator
The inverse — including pack sizing for a stated depth of discharge.
Learn more →Watts to kWh Calculator
Energy from watts and time — what your usable Wh have to cover.
Learn more →Home Battery Siting Checker
Location rules for a home battery install.
Learn more →Home Battery Backup
Accountability around a home battery project.
Learn more →Battery capacity that matches the house
Seamless Home coordinates home battery projects with clear scope and a single point of accountability. Coverage is confirmed per service area rather than promised as blanket availability.
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