⚡kW to Wh Calculator
Live results — type and the math updates instantly. Pick a tab for your direction.
Energy consumed
12,000 Wh
Kilowatt-hours
12 kWh
Joules
43,200,000 J
Kilojoules
43,200 kJ
BTU
40,945.7 BTU
E = 1.5 kW × 1000 × 8 h = 12,000 Wh
kWh to Wh and Wh to kWh quick converter — 1 kWh = 1,000 Wh.
Average power
1.25 kW
Watts
1,250 W
Horsepower
1.68 hp
P = 5,000 Wh ÷ 1000 ÷ 4 h = 1.25 kW
Nominal battery voltage
Amp-hour rating
Device watts
Honest planning, not the lab rating
AC loads lose energy in conversion
Estimated runtime
3.24 h (3 h 14 min)
Nameplate energy
1,200 Wh
Usable energy
972 Wh
Also equals
1.2 kWh
1,200 Wh × 0.90 DoD × 0.90 eff = 972 Wh usable ÷ 300 W = 3.24 h
⚠️ Planning figure, not a promise. Cold weather, battery age, inverter standby draw, and devices that cycle (fridges, pumps) all reduce real runtime. Keep a 10–20% safety margin.
Total watts to protect
Hours of backup needed
UPS conversion loss
Battery energy required
1,333 Wh
In kWh
1.33 kWh
≈ 12V batteries
≈ 2 × 12V 100Ah
Runtime check
2 h at 600 W
600 W × 2 h ÷ 0.90 eff = 1,333.33 Wh battery needed
💡 Sizing rule of thumb: size the UPS/battery for the usable Wh, then buy ~25% headroom above that for battery aging and surge loads (motors, compressors) that briefly draw 2–3× their rating at startup.
📐The kW to Wh Formula
One multiplication. The only thing that ever goes wrong is forgetting the time.
E(Wh) = P(kW) × 1000 × t(h)
Energy in watt-hours equals power in kilowatts, times one thousand (kilo means 1,000), times the duration in hours. Reverse it to find average power: P(kW) = E(Wh) ÷ 1000 ÷ t(h).
kW vs kWh vs Wh — the distinction that matters
kW (kilowatt) is power: the rate energy flows right now, like a car's speedometer. Wh (watt-hour) is energy: power sustained over time, like distance traveled. kWh is simply 1,000 Wh — the unit printed on electricity bills. A 2 kW heater is always a 2 kW heater; run it 3 hours and it has consumed 6,000 Wh (6 kWh) of energy.
💡 "Watts per hour" is not a real unit. W/h would mean power changing over time. What people mean is watts times hours — the watt-hour (Wh). Saying a heater uses "2,000 watts per hour" almost always means it draws 2,000 W continuously: 2,000 Wh per hour of use.
Which horsepower?
The hp option uses mechanical horsepower: 1 hp = 0.7457 kW = 745.7 W, the standard for motors and engines. Metric horsepower (PS/CV) is 0.7355 kW — about 1.4% lower, negligible next to real-world load variation.
📊kW to Wh Conversion Table
Common power × time combinations. Every value = kW × 1000 × hours.
| Power | Time | Energy (Wh) | Energy (kWh) |
|---|---|---|---|
| 0.5 kW | 1 hour | 500 | 0.5 |
| 1 kW | 1 hour | 1,000 | 1 |
| 1.5 kW | 1 hour | 1,500 | 1.5 |
| 2 kW | 1 hour | 2,000 | 2 |
| 3 kW | 1 hour | 3,000 | 3 |
| 5 kW | 1 hour | 5,000 | 5 |
| 10 kW | 1 hour | 10,000 | 10 |
| 1.5 kW | 8 hours | 12,000 | 12 |
| 2 kW | 8 hours | 16,000 | 16 |
| 1 kW | 24 hours | 24,000 | 24 |
| 2 kW | 24 hours | 48,000 | 48 |
✏️Worked Examples
Hand-verified, step by step. Try them in the calculator above.
Example 1 — Air conditioner: 1.5 kW for 8 hours
E = 1.5 × 1000 × 8 = 12,000 Wh (12 kWh = 43,200,000 J).1.5 kW × 1000 × 8 h = 12,000 Wh
Reality check: an inverter AC cycles its compressor, so average draw is usually below the 1.5 kW nameplate — treat 12,000 Wh as an upper bound.
Example 2 — Battery runtime: 12V 100Ah running a 300 W load
Nameplate: 12 V × 100 Ah = 1,200 Wh. Usable with 90% depth of discharge and a 90% efficient inverter: 1,200 × 0.9 × 0.9 = 972 Wh. Runtime: 972 ÷ 300 = 3.24 h (3 h 14 min).12×100 = 1,200 Wh → ×0.9×0.9 = 972 Wh → ÷300 W = 3.24 h
Example 3 — Reverse: 5,000 Wh used over 4 hours
P = 5,000 ÷ 1000 ÷ 4 = 1.25 kW average power (≈1,250 W, ≈1.68 hp).5,000 Wh ÷ 1000 ÷ 4 h = 1.25 kW
🔋Battery Watt-Hours: V × Ah
Amp-hours alone can't compare batteries — voltage matters.
Wh = V × Ah
A 12V 100Ah battery and a 48V 100Ah battery look similar on the Ah rating, but store very different energy: 12 × 100 = 1,200 Wh vs 48 × 100 = 4,800 Wh. Watt-hours are the honest way to compare. This Ah to Wh conversion (Wh = V × Ah) is exactly what the Battery tab computes. (A "12V" LiFePO₄ pack is really 12.8 V nominal: 12.8 × 100 = 1,280 Wh.)
| Battery | Math | Energy |
|---|---|---|
| 12V 100Ah lead-acid | 12 × 100 | 1,200 Wh |
| 12.8V 100Ah LiFePO₄ | 12.8 × 100 | 1,280 Wh |
| 24V 200Ah | 24 × 200 | 4,800 Wh |
| 48V 100Ah | 48 × 100 | 4,800 Wh |
| Power bank 3.7V 20,000mAh | 3.7 × 20 | 74 Wh |
| Laptop 11.1V 5,200mAh | 11.1 × 5.2 | 57.72 Wh |
💡 Airline limit you should know: most airlines cap spare lithium batteries at 100 Wh in carry-on (up to 160 Wh with airline approval) — which is why power-bank Wh ratings are printed on the label. A 74 Wh power bank flies; a 1,200 Wh "solar generator" does not.
🔍Honest Limitations
The arithmetic is exact. The real world is not — here's where the gap lives.
- Constant power assumed. The formula multiplies one power number by time. Real devices cycle — fridges, ACs, and pumps draw far less on average than their nameplate rating.
- Nameplate ≠ average. Appliance labels show maximum draw. A "1.5 kW" heater on a thermostat may average 0.9 kW.
- Battery estimates are planning figures. Depth of discharge and inverter efficiency are rules of thumb, not guarantees. Cold weather, battery age, and standby draw all shave off runtime — keep a 10–20% margin.
- No Peukert modeling. Lead-acid batteries deliver less total energy at high discharge rates; this calculator uses a flat efficiency instead.
- Not a billing tool. It computes energy, not money. Multiply kWh by your tariff for cost — or use a dedicated electricity cost calculator.
🧭 Where this tool sits (no overlap by design)
- Electricity bill / cost? → needs tariffs and money math — use an electricity cost calculator.
- kW to joules as the main unit? → kW to joules converter (and kW to kilojoules).
- Any energy unit to any other? → a general energy unit converter.
- This page owns the kW + time → Wh workflow: batteries, runtime, and UPS sizing.
❓Frequently Asked Questions
Every answer below is also in the page's structured data.
What is the formula to convert kW to Wh?
Energy in watt-hours equals power in kilowatts times 1,000 times time in hours: E(Wh) = P(kW) × 1000 × t(h). For example, a 1.5 kW air conditioner running 8 hours uses 1.5 × 1000 × 8 = 12,000 Wh. The calculator above shows each substitution step so you can verify the math.
Can you convert kW to Wh without knowing the time?
No. Kilowatts measure power (the rate of energy use), while watt-hours measure energy (power × time). 1 kW running for one hour is 1,000 Wh, but 1 kW running for ten minutes is only about 167 Wh. Any converter that gives you Wh from kW alone is silently assuming a time period — usually one hour.
How many watt-hours are in 1 kW?
Per hour of operation: 1,000 Wh. That is the same as 1 kWh, since the kilo prefix means 1,000. If the question is really about a different time span, multiply 1,000 Wh by the number of hours: 1 kW for 30 minutes is 500 Wh, and 1 kW for 24 hours is 24,000 Wh.
How do I convert Wh back to kW?
Divide watt-hours by 1,000 and then by the hours: P(kW) = E(Wh) ÷ 1000 ÷ t(h). For example, 5,000 Wh consumed over 4 hours means an average power of 5,000 ÷ 1000 ÷ 4 = 1.25 kW. Use the Reverse tab above — it does this for any time unit.
What is the difference between kW, kWh, and Wh?
kW (kilowatt) is power — how fast energy flows right now, like the speedometer of a car. Wh (watt-hour) is energy — power sustained over time, like distance traveled. kWh is simply 1,000 Wh, the unit on electricity bills. A 2 kW heater has a power rating of 2 kW; run it for 3 hours and it consumes 6,000 Wh, i.e. 6 kWh, of energy.
How many watt-hours does a 12V 100Ah battery hold?
1,200 Wh. Battery energy is voltage times amp-hours: 12 V × 100 Ah = 1,200 Wh (1.2 kWh). Note that a 12V-class LiFePO4 battery is actually 12.8 V nominal, so its true nameplate energy is 12.8 × 100 = 1,280 Wh. Usable energy is lower — see the depth-of-discharge question.
How do I convert amp-hours (Ah) to watt-hours (Wh)?
Multiply amp-hours by the battery voltage: Wh = V × Ah. A 48V 100Ah battery stores 4,800 Wh — four times the 1,200 Wh of a 12V 100Ah battery — which is why Ah alone cannot compare batteries of different voltages. The Battery tab applies this formula and adds a runtime estimate.
How long will my battery or UPS run a given load?
Divide usable watt-hours by the load in watts: runtime (h) = usable Wh ÷ W. Start from nameplate Wh (V × Ah), multiply by a realistic depth of discharge (about 50% for lead-acid, 80–90% for LiFePO4), then multiply by inverter efficiency (about 90% for AC loads). Example: 1,200 Wh × 0.9 × 0.9 = 972 Wh usable; a 300 W load runs about 3.24 hours.
What depth of discharge should I assume for runtime planning?
For long battery life, plan around 50% of rated capacity for lead-acid/AGM and 80–90% for LiFePO4. Nameplate Wh is a laboratory rating; regularly draining a lead-acid battery to zero shortens its life dramatically, and cold weather plus inverter standby draw shave off more. The Battery tab lets you pick a preset instead of guessing.
Is 'watts per hour' a real unit?
No — 'watts per hour' (W/h) would mean power changing over time, which is not what anyone means. The correct unit for energy used over time is the watt-hour (Wh): watts multiplied by hours, not divided. Saying a heater uses '2,000 watts per hour' almost always means it draws 2,000 W continuously, i.e. 2,000 Wh per hour of use.
How many watt-hours does a 1.5 kW air conditioner use in 8 hours?
12,000 Wh (12 kWh). The math: 1.5 kW × 1000 × 8 h = 12,000 Wh. In practice an inverter AC cycles its compressor, so the average draw is often lower than the nameplate 1.5 kW — treat this as an upper bound unless you know the duty cycle.
Can this calculator estimate my electricity bill?
It gives you the energy half of the bill (Wh/kWh); it does not compute money. Multiply the kWh result by your tariff (for example $/kWh or Rp/kWh) to get cost. For a full bill estimate with tariffs, tiers, and appliance profiles, use a dedicated electricity cost calculator — this tool deliberately stays money-free so the unit math stays exact.
Which horsepower does the hp input use?
Mechanical horsepower: 1 hp = 0.7457 kW = 745.7 W. That is the standard used for motors and engines. Metric horsepower (PS/CV) is slightly different at 0.7355 kW; if your equipment is rated in PS, the result will be about 1.4% high — negligible next to real-world load variation.
How is this different from a general energy unit converter?
A general energy unit converter translates between energy units (Wh, joules, BTU, calories) without any notion of time or load. This tool is a workflow: it starts from power and duration — the two numbers you actually have on an appliance label or battery — and works forward to energy, or backward to runtime and UPS sizing, including battery chemistry realities like depth of discharge.
What about converting kW to joules or kilojoules?
Those are energy-unit conversions that need a time span too: 1 Wh = 3,600 J exactly. This page shows joules, kilojoules, and BTU as secondary outputs for every calculation, but if joules are your primary unit, a dedicated kW-to-joules tool keeps the focus there instead of on watt-hours and batteries.
How accurate is this calculator?
The arithmetic is exact — it is multiplication and division on your inputs, with no rounding until display. Real-world accuracy depends on your inputs: appliance labels show maximum, not average, power; devices cycle on and off; battery depth of discharge and inverter efficiency are planning estimates, not guarantees. Treat battery runtimes as planning figures with a 10–20% safety margin.