An appliance wattage calculator answers a question that comes up whenever electricity has to come from something other than a wall socket: how much power does this list of things need, all at once, and how much energy do they get through in a day? That is the number you need before buying a generator, sizing an inverter for a van or a boat, working out whether a circuit will trip, or deciding what a power cut actually costs you in lost freezer contents.
Arb Digital keeps a free tools library for the practical arithmetic behind household and small-business decisions. This page is deliberately the load-list half of the problem. It does not price your whole electricity bill and it does not size a battery bank — it produces the watt and kilowatt-hour figures that every one of those calculations starts from.
What This Appliance Wattage Calculator Does
Name up to six appliances, enter the running watts from each nameplate, a surge multiplier for anything with a motor or compressor, the hours it runs on a typical day and a quantity. The tool returns the total running load in watts, the peak surge load, the energy the list consumes per day and per month, and the current in amps at your supply voltage. The bars rank the four biggest energy consumers, which is often not the same ranking as the four biggest wattages.
Two boundaries are worth stating, because three adjacent tools on this site answer neighbouring questions. The electricity bill calculator takes your usage and turns it into a priced bill with standing charges and tariffs — it is about money, this page is about load. The battery life calculator tells you how long a battery of a known capacity will run a known load; this page produces that load. And the generator size calculator converts a load list into a generator rating with the headroom rules applied. Use this page first, then whichever of those three you need.
How to Use It
- Replace the placeholder wattages. The values the page loads with are editable placeholders, not data about your appliances. Every real figure is on the nameplate — usually a sticker on the back, base or inside the door.
- Set a surge multiplier for anything with a motor. Fridges, freezers, air conditioners, pumps, compressors and washing machines draw far more current for the first second or two. Anything purely resistive — a kettle, a toaster, an incandescent lamp — stays at 1.
- Enter running hours, not hours plugged in. A fridge is powered 24 hours a day but its compressor runs perhaps a third of that. See the duty-cycle section below.
- Set the supply voltage. This only affects the amps figure, but the amps figure is what tells you whether a circuit or an extension lead is being asked for too much.
- Read both headline numbers. Running watts is what a supply must sustain; peak surge is what it must survive for a moment without stalling or shutting down.
The Formula / How It's Calculated
Running load is a plain sum: Σ (watts × quantity). Energy per day is Σ (watts × quantity × hours) ÷ 1,000 to convert watt-hours into kilowatt-hours, which is the same relationship the NIST reference on metric (SI) prefixes describes for the kilo prefix. Monthly energy multiplies the daily figure by 30.44, the average month length. Current is watts ÷ volts.
Peak surge is the only line that is not a straight sum, and it is the one people get wrong. Adding every appliance's surge together assumes all six motors start in the same instant, which does not happen and produces a wildly oversized answer. The realistic worst case is that the largest surge starts while everything else is already running normally, so the calculation is total running load − that appliance's running watts + that appliance's surge watts, evaluated for every appliance and the largest result taken.
Worked example, using the values the page loads with. Running watts are 150 + 900 + 1,100 + 60 + 150 + 500 = 2,860 W. Daily energy is (150×8) + (900×6) + (1,100×0.3) + (60×5) + (150×5) + (500×0.7) = 8,330 Wh = 8.33 kWh, which is 253.6 kWh a month. At 230 V the running current is 2,860 ÷ 230 = 12.4 A. For peak surge, the air conditioner is the biggest offender: 2,860 − 900 + 2,700 = 4,660 W. The washing machine gives only 3,860 W, so 4,660 W governs.
Duty Cycle: Why Hours Plugged In Is the Wrong Number
The largest error in most load lists is entering 24 hours for a refrigerator. A fridge is energised continuously, but its compressor is thermostatically controlled and only runs when the cabinet needs cooling. Enter the hours the compressor actually runs — the equivalent full-power hours — not the hours the plug is in the wall. The same applies to freezers, air conditioners, electric heaters, water heaters, well pumps and anything else with a thermostat or a float switch.
Getting that figure honestly is easiest with a plug-in energy meter, which reports kilowatt-hours over a period. Divide the kilowatt-hours by the appliance's rated kilowatts and you have its equivalent full-power hours. A fridge that used 0.9 kWh in a day at a 150 W rating ran the equivalent of six hours. Without a meter, remember that the duty cycle rises sharply in hot weather and falls in cold, so a summer measurement is not a winter one.
The opposite error is entering a duty cycle for something that has none. A television at 150 W really does draw about 150 W for every one of the five hours it is on. Resistive and electronic loads are honest in a way motors are not.
Nameplate Watts, Real Watts and Power Factor
The wattage printed on a nameplate is the maximum the appliance is designed to draw, not the average it draws in use. A 1,100 W microwave is drawing close to 1,100 W the whole time it is cooking, so nameplate and reality agree. A 2,000 W vacuum cleaner on a low setting is not. Where the two differ, use a measured figure if you have one and the nameplate if you do not — the nameplate errs high, which is the safe direction for sizing a supply.
Some nameplates give volts and amps instead of watts. Multiply them: 230 V × 4.3 A is roughly 990 W. For motor-driven appliances that product overstates real power somewhat, because current and voltage fall out of step — the ratio between real power in watts and apparent power in volt-amps is the power factor, and it is why generator and UPS ratings are often quoted in VA rather than W. The electrical power calculator handles that conversion properly, and the Ohm's law calculator covers the volts, amps, ohms and watts relationships underneath it.
What the Amps Figure Is Actually Telling You
Watts tell you about energy; amps tell you about wire. A circuit breaker, an extension lead and a plug fuse are all rated in amps, and every one of them trips or fails on current regardless of how efficiently the energy is being used. A 2,860 W load at 230 V is 12.4 A, comfortably inside a typical 16 A circuit. The identical load at 120 V is 23.8 A, which exceeds a standard 15 A circuit and would need a dedicated 30 A run.
That halving of current as voltage doubles is why the same appliance list is far more demanding in a 120 V country than a 230 V one, and why large appliances in North America are wired to 240 V circuits. When you total a load list, check the amps against the specific circuit the load will sit on, not against the whole house supply. Six appliances totalling 12 A is fine spread over three circuits and a problem on one.
From Load List to Energy Cost and Emissions
The monthly kilowatt-hour figure is the bridge to everything else. Multiplied by your unit rate it gives an energy cost, though a real bill also carries standing charges, tiered rates and taxes that the electricity bill calculator handles. It is also the input to any efficiency comparison: the LED savings calculator works on exactly this basis for lighting, and the solar panel calculator needs annual kilowatt-hours to size an array.
For context on where household electricity goes, the US Energy Information Administration's explainer on electricity use in homes reports that air conditioning, space heating and water heating were the three largest residential end uses in 2020, at 19%, 12% and 12% respectively. If your load list does not have a thermal appliance near the top of the bars, it is probably incomplete. Kilowatt-hours also convert to emissions: the EPA's greenhouse gas equivalencies references give a US national average of about 3.94 × 10⁻⁴ metric tons of CO₂ per kilowatt-hour consumed.
Arb Digital's free tools library covers the energy, cost and planning maths behind household and small-business projects, and our team is happy to talk through anything the tools cannot answer.
Browse Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Entering 24 hours for a fridge or freezer — enter the equivalent hours the compressor runs, which is usually a third of the time or less.
- Adding every surge together — motors do not start simultaneously, and summing surges produces a supply two or three times larger than anything you need.
- Ignoring surge entirely — a supply sized only on running watts will stall or trip the first time a compressor kicks in.
- Using the placeholder wattages as data — they exist so the page shows a working example. Your appliances have their own nameplates.
- Checking amps against the whole house instead of one circuit — breakers trip per circuit, and a load list concentrated on one socket is the usual cause.
Related Free Tools From Arb Digital
Use the generator size calculator once you have a load list, the battery life calculator to find how long a battery sustains that load, the battery capacity calculator to convert between mAh, Ah and watt-hours when sizing a pack, the energy converter for kWh to joules, BTU or therms, and the electricity bill calculator to turn the monthly kilowatt-hours into money. Everything else is in the free online tools hub.
Frequently Asked Questions
On the nameplate, which is normally a sticker or engraved panel on the back, the base, or inside the door. If it lists volts and amps instead of watts, multiply the two. The values this page loads with are editable placeholders, not figures for your appliances.
Running watts is the steady draw once an appliance is up to speed. Surge watts is the much larger draw for the first second or two while a motor or compressor starts. A supply must sustain the running figure and survive the surge figure.
Because motors do not all start in the same instant. The realistic worst case is the largest motor starting while everything else already runs normally, so the tool takes the total running load, removes that appliance's running watts and adds its surge instead.
The equivalent hours its compressor runs, not the hours it is plugged in. A plug-in energy meter gives this directly: divide the kilowatt-hours it recorded by the appliance's rated kilowatts. Duty cycle rises in hot weather and falls in cold.
Because current is watts divided by volts. Halving the voltage doubles the current for the same power, which is why large appliances in 120 V countries are wired to 240 V circuits and why the same load list stresses a North American circuit far more.
No. It produces the running and surge load a generator would have to meet. Turning that into a generator rating involves headroom, altitude and fuel-type adjustments, which the generator size calculator on this site handles separately.
That tool prices a whole household's consumption, including standing charges and tariff tiers. This one builds the appliance load list underneath it and reports watts, surge watts and kilowatt-hours rather than a bill.
This tool performs arithmetic on figures you supply. It is not electrical design advice, does not account for wiring, protection or local regulations, and any installation work should be specified and carried out by a qualified electrician.
