Appliance Power Draw Chart: Watts to Amp-Hours at 12V

Nobody runs all of those at once, and the total is there to make a point rather than to be used: the always-on column alone can exceed a 100Ah lithium battery's entire usable capacity of 85 amp-hours. Look at the inverter idle row in particular. Fifteen watts of an inverter doing absolutely nothing, left switched on for 24 hours, costs 30 amp-hours, which is more than the fridge. That single row is the most common reason a system that should work does not, and the fix is a switch.

Now read the amps column and the daily Ah column side by side, because they tell opposite stories. The hair dryer pulls 142A, which is a genuinely alarming current that needs 2/0 cable and a 200A fuse, and it costs 14 amp-hours a day. The blender pulls 47A and costs 1.4 amp-hours. The coffee grinder pulls 14A and costs 0.3. Meanwhile the fridge pulls 3.75A and costs 31.5.

The lesson is worth stating plainly because it is the single most useful idea on this page: nameplate watts size the inverter, the cable and the fuse. Duty cycle sizes the battery. They are two different questions with two different answers, and treating them as one is why people buy 3000W inverters they cannot feed and 100Ah batteries that cannot last a night. The inverter sizing calculator answers the first question and the battery bank calculator answers the second.

Two intermittent loads deserve special mention. The winch row is not really a house-battery load at all: a winch runs off the starter battery with the engine running and the alternator contributing, and the 20 amp-hours shown is the energy involved rather than a call on your house bank. And the induction burner at 71 amp-hours for half an hour of cooking is the row that decides whether a build cooks on electricity or on propane, because 71 amp-hours a day is most of a 100Ah battery gone before anything else has run.

How much does the inverter cost you in losses?

Between 10 and 15 percent of everything that passes through it, plus an idle draw that never stops. A good pure sine inverter under a reasonable load is around 88 to 92 percent efficient, and efficiency falls off badly at very light loads, so a 2000W unit running a 20W phone charger can be operating at well under half its rated efficiency.

A laptop is the clearest case, because there are two genuinely different ways to charge it. The table below charges the same laptop with the same 60W for the same three hours by three different routes.

The USB-C route does one conversion, from 12V DC to 20V DC, at about 88 percent. The inverter route does two, from 12V DC up to 120V AC at about 88 percent and then back down to DC inside the laptop brick at about 90 percent, for roughly 79 percent overall. That difference is about 2 amp-hours a day for one laptop, which is small enough to ignore on its own. The idle row is where it stops being small: the same charge with the inverter left running for another nine hours afterwards costs 34 amp-hours instead of 17.

The practical answer is a 12V USB-C Panel Mount Socket, 65W PD and QC3.0 (83W total) , which delivers 65W of USB-C Power Delivery straight from 12V and removes the inverter from the equation for laptops, tablets, phones, headlamps, camera batteries and increasingly monitors. Keep the inverter for the things that genuinely need AC. When you do need one, idle draw matters as much as peak output: a Victron Energy Phoenix 1200VA 12V Pure Sine Wave Inverter costs more than a budget 2000W unit and delivers less peak power, and is still the better buy in a full-time build precisely because it can be left switched on without quietly eating the battery. The inverter roundup compares idle draw across the range, and the pure sine versus modified sine comparison covers the waveform question.

What does a realistic daily budget look like?

Three worked examples, built from the rows above. These are the three shapes most builds fall into, and the jump between them is much larger than people expect.

A 100Ah LiFePO4 battery holds 1,280Wh and gives up 85 percent of it safely, which is 85 usable amp-hours. The weekend build at 50 amp-hours a day gets a comfortable night and most of a second. The full-time build at 106 amp-hours a day needs 200Ah to hold two days with any margin. The cooking build at 206 amp-hours a day needs 400Ah, which is most of 200 lb of battery and a payload question as much as a power question. Check that against the payload weight calculator before you order anything, because the door jamb sticker is a harder limit than the battery budget.

The other half of the equation is replacement. Roughly 400W of roof solar delivers about 125 amp-hours a day at five peak sun hours with a realistic derate, which covers the full-time build in good conditions and does not cover the cooking build at all. The solar output chart works through that arithmetic and the sun hours by region chart tells you which column applies where you actually travel.

Which numbers on this page are most likely to be wrong for you?

The fridge, by a wide margin, and it is the biggest line in most budgets. The 31.5 amp-hours shown assumes a 35 percent duty cycle, which is a mild-weather figure. The same ICECO VL45 45L Portable Refrigerator (Secop Compressor) in 95F ambient can run at nearly a 60 percent duty cycle and cost 50 amp-hours or more, and a poorly insulated box in the sun is worse again. The fridge draw by ambient temperature chart gives the full curve, and if you camp anywhere hot it is the more useful page.

Second, the parasitic loads nobody lists. A battery monitor, a propane detector, a carbon monoxide alarm, a solar controller, a fridge control board and half a dozen Bluetooth radios together commonly account for 5 to 15 amp-hours a day. That is a range rather than a figure because it genuinely varies by an order of magnitude between builds. The only way to know your own is to measure it, which is what a Victron SmartShunt 500A Battery Monitor is for: it counts every amp-hour in and out, including the ones you did not know about. A AstroAI Digital Clamp Meter, AC/DC Current and Voltage (4000 count) lets you chase an individual circuit once the shunt tells you something is wrong.

Third, heating and cooling, which are excluded from every budget above on purpose. A diesel air heater is included at 15W running average because it burns fuel rather than electricity and only the fan and glow plug draw from the battery. Anything that makes heat or cold electrically is a different category entirely: air conditioning on a 12V system is measured in hundreds of amp-hours a day, and there is no version of that arithmetic where a 200Ah bank is enough.

Fourth, the battery you actually own. A Litime 12V 100Ah LiFePO4 Battery (Group 24) gives 85 usable amp-hours of its 100Ah nameplate, an AGM of the same nameplate gives 50, and a lead acid battery drawn below half is a battery you are destroying. The battery chemistry comparison chart lays out the usable capacity per chemistry, which is the number that turns this page's daily total into a battery size.

Everything here is calculated from published manufacturer specifications and typical published duty cycles rather than measured by us, and it is researched guidance rather than an electrical certification. Confirm current draw against the manual for your own appliances before sizing cable or fuses from it, and have any lithium installation inspected by a qualified installer before it carries load.

Where to go next

• Power consumption calculator, this table with your own hours in it.
• Fridge power draw by temperature, the biggest and most variable line in the budget.
• Solar panel output by sun hours, the replacement side of the same arithmetic.
• Battery bank calculator, turning a daily total into a bank size.
• How to size a battery bank, the full method end to end.