Build the overlap stack
List the AC loads that may run at the same time instead of sizing around one favorite appliance.
Inverter planning
RV inverter size calculator
Estimate the inverter size, startup surge, DC current, and battery runtime before a heavy AC load turns into a cable, fuse, or battery-discharge problem.
Quick inverter read
The inverter target works, but DC current is the hard part
The listed AC loads total 2,240W running and about 2,840W at startup. A 3,000W continuous inverter with roughly 3,500W surge is the planning target.
Continuous inverter
3,000W
2,800W design load after factor
Surge target
3,500W
2,840W estimated startup stack
DC current
259.3A
1.3 hr estimated battery runtime
Treat the inverter label as the start of the wiring conversation. Confirm the manual cable table, fuse class, battery discharge limit, transfer switching, ventilation, and grounding before installing.
Keep surge separate
Continuous watts keep loads running. Surge watts decide whether a motor or compressor starts cleanly.
Follow the current
Once inverter watts rise, battery cables, fuses, lugs, and terminals become part of the answer.
Start over
This calculator stores inputs locally in this browser. Clear saved inputs when stale values are getting in the way.
Inverter size calculator
Size the inverter around simultaneous AC loads, surge, and DC current.
Add the AC loads that may run at the same time. The calculator estimates continuous inverter watts, startup surge, DC-side current, fuse planning, and rough battery runtime for the entered load stack.
Inverter sizing estimate
The inverter target works, but DC current is the hard part
The listed AC loads total 2,240W running and about 2,840W at startup. A 3,000W continuous inverter with roughly 3,500W surge is the planning target.
Continuous inverter
3,000W
2,800W design load after factor
Surge target
3,500W
2,840W estimated startup stack
DC current
259.3A
300A planning fuse floor
Battery runtime
1.3 hr
3.2 kWh usable bank estimate
System checks
Running load
2,240W
All listed loads at entered quantity
Largest surge delta
600W
Added on top of running load
Target battery
250Ah
1.0 hr at 12V lithium
Surge DC current
263A
Momentary planning estimate
Watch-outs
This is an inverter planning estimate. Final inverter size, wiring, fuse class, transfer switching, ventilation, grounding, and installation details should follow manufacturer instructions and applicable codes.
Startup surge is estimated as all listed running loads plus the single largest surge delta. If multiple motors or compressors start together, real surge can be higher.
The DC current is high. Short cable runs, correct fuse class, proper lugs, and possibly a 24V or 48V architecture matter more as inverter size rises.
Recommended next move
Open the wire-size calculator next and check whether the DC cable path, fuse, and battery terminals can support the current.
Why this exists
Inverter shopping gets expensive when you ignore the DC side.
A 2,000W or 3,000W inverter can make normal household loads feel possible in an RV, but the battery bank still has to supply the current. This calculator connects the appliance list to the surge rating, battery runtime, and wire-size conversation.
This is sizing math, not wiring approval.
Still verify inverter manuals, battery discharge limits, cable length, fuse class, transfer equipment, grounding, ventilation, and qualified electrical requirements.
Use this with
DC wire size calculator
Use this after the inverter estimate to check the battery-cable current and voltage-drop pressure.
Battery sizing calculator
Use this when inverter runtime depends on the whole daily load list, not just the heavy AC appliance.
Best RV inverter chargers
Use this when the planning target is clear and you are ready to compare inverter-charger fit.
AC battery runtime calculator
Use this when the inverter load is specifically rooftop AC and solar-assisted cooling runtime.
Tool notes
What the inverter-size estimate is actually saying
This output is a planning estimate for AC appliance overlap, startup surge, DC current, and battery runtime. It does not replace inverter manuals, fuse coordination, transfer-switch design, or qualified electrical work.
Simultaneous running watts
The calculator adds every listed running load at the entered quantity because the inverter has to carry the overlapping AC load, not just the largest appliance.
Startup surge
Startup is estimated as the total running load plus the largest single surge delta. That matches the common case where one motor or compressor starts while other loads are already running.
DC-side current
AC watts are divided by battery voltage and inverter efficiency. This is why a 3,000W inverter can create very large 12V cable and fuse requirements.
Battery runtime
Runtime uses the entered battery amp-hours, voltage, chemistry usable-depth assumption, and inverter efficiency. It is a planning estimate, not a promise that every battery can deliver the peak current.
Avoid these traps
Common mistakes before buying
Sizing the inverter from one appliance label
A microwave label does not include the laptop, router, converter, coffee maker, or fan that may already be running. The overlap is what trips marginal systems.
Ignoring 12V current
A large inverter may look easy from the AC side, then require short, heavy DC cable, the right fuse class, and battery terminals that can safely support the current.
Buying surge rating instead of changing load timing
If startup surge drives the recommendation, a soft-start device or not running two heavy loads together can be cheaper than buying a much larger inverter.
Treat the calculator result as a planning range, then verify the relevant manufacturer guidance, safety limits, installation requirements, and local rules before changing the rig.See assumptions
Gear to compare after the math
Spec-checked products to compare after the math.
These handoffs match the calculator family, not a one-click prescription. Verify fit, specs, clearances, and install limits before buying.
SOK SK12V100P 12V 100Ah LiFePO4 Battery
Best for
Budget lithium builds after a smaller bank result
A common 100Ah building block when the calculator result still fits a straightforward 12V lithium bank.
Current listing
SOK SK12V100P 12V 100Ah LiFePO4 Battery at SOK.
- Checked model
- SK12V100P
- Spec fit
- A 100Ah LiFePO4 building block for smaller 12V banks when the calculator result is framed around modular battery count and charger compatibility.
Victron SmartShunt 500A/50mV
Best for
Making battery runtime visible instead of guessed
A shunt-based monitor is the usual next buy when the calculator result depends on real state-of-charge tracking.
Current listing
Victron SmartShunt 500A/50mV at Victron.
- Checked model
- SmartShunt 500A/50mV
- Spec fit
- A shunt-based monitor handoff when calculator results depend on real state-of-charge and consumed amp-hours instead of voltage guessing.
Victron Orion XS 12/12-50A DC-DC Battery Charger
Best for
Improving recharge support for larger daily loads
Use this class of DC-DC charger when the battery answer only works if drive-day recovery is part of the plan.
Current listing
Victron Orion XS 12/12-50A DC-DC Battery Charger at Victron.
- Checked model
- Orion XS 12/12-50A
- Spec fit
- A 50A DC-to-DC charger handoff when route-day charging is part of the battery recovery plan and alternator reserve is verified.
Frequently asked
Questions RVers usually ask next.
What size inverter do most RVers need?
Small work and charging loads may only need 600W to 1,000W. Microwaves, coffee makers, and induction cooking often push the answer into the 2,000W to 3,000W range. Air conditioning usually needs both a larger inverter and a serious battery and wire plan.
Does a bigger inverter mean longer battery runtime?
No. A bigger inverter only increases the load it can serve. Runtime comes from usable battery watt-hours, inverter efficiency, and how many watts the AC loads consume.
Should I size by continuous watts or surge watts?
You need both. Continuous watts cover the loads after they are running, while surge watts cover startup events from motors, compressors, and some kitchen appliances.
Why does the calculator recommend checking wire size next?
The DC side is often the hidden constraint. Once inverter watts rise, the battery cable, fuse, lug, disconnect, and terminal ratings become as important as the inverter label.