The 12-Volt Inverter Decision Tree
Inverter sizing is one of those decisions that's easy to get wrong. Too small and the kettle trips the inverter every morning. Too big and you've spent money on capacity you'll never use, plus an idle-current penalty draining the bank 24/7.
What runs on what
| Appliance | Typical draw | Inverter spec |
|---|---|---|
| Laptop, phone charger | 30–100W | 300W enough |
| Small kitchen appliance (blender, hand mixer) | 200–600W | 800W |
| Espresso machine | 800–1,400W | 1,500W+ |
| Microwave | 900–1,500W | 1,800W+ |
| Power tools (drill, jigsaw) | 500–1,200W | 1,500W with surge |
| Induction cooktop | 1,400–2,200W | 2,500W+ |
| Air conditioning (small) | 800–1,500W run; 3,000W surge | 3,000W+ with surge handling |
The sizing rules
- Add up worst-case simultaneous loads. Don't add the peak of each item; account for what actually runs at once.
- Account for surge capacity. Motors (pumps, compressors) draw 3–5x rated power at startup.
- Match to battery bank. A 2,000W inverter pulling from a 200Ah bank will trip low-voltage shutdown.
- Account for AC wiring. 30A AC service is the practical ceiling for most cruising boats.
Pure sine vs modified sine
Pure sine wave for any modern electronics, induction motors, or anything with sensitive controls. Modified sine is cheaper but works only for resistive loads (kettle, basic lights). The price difference is small; pure sine is the default in 2026.
Inverter-charger combinations
Victron Multiplus and similar inverter-charger units have become standard. They handle inverting from battery to AC, charging from shore power, transfer switch between sources, and pass-through. Single-unit elegance vs separate inverter + separate charger.
What cruisers actually buy
- Couples cruising with espresso/microwave/laptops: 1,500–2,000W pure sine
- Liveaboards with induction cooking: 3,000W+ inverter-charger
- Family boats with all-electric ambitions: 5,000W+ Multiplus, big lithium bank
- Minimalists running 12V DC: 300–600W small unit for occasional AC needs
Costs
| Size | Range (USD) |
|---|---|
| Pure sine 300W | $100–250 |
| Pure sine 1,500W | $400–800 |
| Pure sine 2,000W | $500–1,000 |
| Victron Multiplus 3000W | $1,400–2,000 |
| Victron Multiplus 5000W | $2,200–3,200 |
Frequently asked questions
Right size?
Sum worst-case simultaneous loads + surge capacity for motors.
Pure sine necessary?
Yes for modern electronics and motors. Default in 2026.
Inverter-charger combo?
Cleaner installation, slightly higher cost. Worth it for serious systems.
Cost?
$100 for 300W up to $3,200 for 5000W Multiplus.
Battery bank to support it?
Roughly 50–100% of inverter peak rating in usable Ah at 12V.