kWh/100 km is how much energy an EV uses to travel 100 km. Lower is better. It turns into range by dividing your usable battery energy by that number, and into cost by multiplying by your electricity price and allowing for charging losses. Real-world efficiency swings a lot with speed, temperature, heating/AC, hills, weight, tyres, charging method, and battery ageing. Below, you’ll learn what the number means, why WLTP/EPA labels can mislead, how to do the simple maths, where the traps are, and how to drive your costs down.

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Efficiency - the hidden metric that determines real-world range and cost.

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Why doesn’t my EV’s “range” match the brochure?

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If you’ve ever bought an EV on the promise of a big WLTP range only to see the number tumble on the motorway, you’re not alone. A mate in Melbourne picked a large SUV because it boasted 550 km on paper; on family trips at 110 km/h with a roof box, it behaved like a 350-380 km car. Frustrating.

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Here’s the uncomfortable truth: chasing headline range or battery size is yesterday’s logic. In NZ and Australia, most spec sheets show WLTP, which is optimistic for open-road speeds and summer-hot or winter-cold days. The better anchor is efficiency: kWh/100 km. It’s the EV equivalent of litres/100 km. It predicts how far you’ll actually go, what you’ll pay, and how often you’ll stop.

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After years comparing owner logs, independent long-loop tests, and local driving conditions, the pattern is clear. The cars people love long-term aren’t always the ones with the biggest battery; they’re the ones with the best efficiency for how they really drive.

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What does kWh/100 km actually tell you?

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Think of your battery as the tank, and kWh/100 km as how thirsty the car is. Lower equals farther and cheaper.

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Quick maths you’ll actually use:

Range (km) = usable battery (kWh) ÷ (kWh/100 km) × 100.
Cost per 100 km (battery only) = (kWh/100 km) × your electricity price ($/kWh).
Grid cost per 100 km (include charging losses) = (kWh/100 km ÷ charging efficiency) × ($/kWh). Home Level‑2 is often ~90% efficient; DC fast can be ~85-95%.
Conversions: kWh/km = (kWh/100 km) ÷ 100; kWh/100 miles ≈ (kWh/100 km) × 1.609.

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Why does the label mislead-and what should you ask instead?

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The common mistake is assuming official test numbers equal your life. WLTP (common in AU/NZ) tends to overstate range versus steady 100-110 km/h driving. EPA (US) is often closer but still not your exact route. Bigger batteries can hide inefficiency yet cost more, weigh more, and charge slower per kilometre gained.

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Shift your check-list:

Don’t ask: “What’s the WLTP range?” Do ask: “What’s its real‑world kWh/100 km at 100-110 km/h, with AC or heat on?”
Don’t ask: “How big is the battery?” Do ask: “How efficient is the car on my commute and weekend routes?”
Don’t ask: “Does it have fast charging?” Do ask: “What’s my cost per 100 km at home vs public DC, including charging losses?”

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What really changes kWh/100 km on the road?

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Here’s the rational backbone that catches most buyers out:

Typical real‑world bands:
Very efficient sedans/aero‑optimised EVs: ~10-15 kWh/100 km.
Small/midsize EVs: ~15-18 kWh/100 km.
Compact SUVs/family EVs: ~18-22 kWh/100 km.
Large/heavy/luxury: 22-30+ kWh/100 km.
Test cycles differ: WLTP and older NEDC yield rosier numbers than EPA for the same car. AU/NZ buyers commonly see WLTP on stickers.
Speed matters most: Aero drag grows with the square of speed; jumping from 90 to 110 km/h can add several kWh/100 km.
Weather counts: Cold saps battery efficiency and cabin heat draws big watts; hot weather and AC also add load. Winter drops of 10-40% are observed depending on vehicle and prep.
Charging losses are real: Expect roughly 6-15% more kWh from the wall than the car reports using on the road.
Batteries age: Capacity typically declines around 1-2.5% per year on average, so range shrinks slowly even if your kWh/100 km doesn’t change.

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How far will I go-and what will it cost me?

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Let’s do the numbers you’ll actually use.

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Range example:

Car: 75 kWh usable battery, 15 kWh/100 km real‑world.
Range = 75 ÷ 15 × 100 = 500 km.
Cold‑season penalty of 20%? Expect ~400 km on those days.

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Cost examples (using a representative US electricity price, swap in your tariff):

Efficient midsize (15 kWh/100 km), home Level‑2 at $0.165/kWh, 90% efficiency:\n
Grid energy per 100 km = 15 ÷ 0.90 = 16.67 kWh.\n
Cost = 16.67 × $0.165 ≈ $2.75 per 100 km, or $0.0275/km.
Larger EV (22 kWh/100 km), public DC at $0.40/kWh, 92% efficiency:\n
Grid energy = 22 ÷ 0.92 ≈ 23.91 kWh.\n
Cost ≈ 23.91 × $0.40 ≈ $9.56 per 100 km, or ~$0.0956/km.

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Local note: Many NZ/AU households pay roughly mid‑20s to mid‑30s cents per kWh on standard plans. Your actual plan (and solar/TOU rates) will swing the result, so use your bill.

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What does the wrong choice feel like day to day?

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Picture a Friday run from Auckland to Taupō in winter. You set off at 100-110 km/h with the heater going, two kids, and a bike rack. An inefficient SUV that promised 500+ km WLTP now forces two DC stops and costs closer to $9-10 per 100 km on public fast charging. You arrive late, a bit frazzled, and the savings you expected have evaporated.

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Now flip it. A sleeker, more efficient EV at 16 kWh/100 km, heat pump fitted, tyres at the right pressure. You pre‑condition on the driveway while plugged in. One brief stop, lower bill, calmer kids, and you pull in with charge to spare. That’s the emotional dividend of buying for efficiency: fewer interruptions, lower bills, and a car that quietly fits your life.

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Is there a smarter way to choose?

Use the DRIVE framework

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Here’s a practical framework to pin decisions to your reality:

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D Duty cycle: How you actually drive. Typical cruising speed? City vs motorway mix? Hills? Roof rack or towbar?
R Ratings you trust: Align test labels with reality. Find real‑world kWh/100 km at your speeds; treat WLTP as optimistic at 100-110 km/h.
I Infrastructure and cost: Where you’ll charge and what you pay. Home/work L2 vs DC fast, plan rates, solar availability, and charging efficiency.
V Vehicle tech: Efficiency features that matter. Aero design, heat pump, efficient tyres, brake regen controls, thermal pre‑conditioning.
E Economy target: Pick a number and sanity‑check it. Set a kWh/100 km target that delivers your range within your budget.

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Ask any salesperson or spec sheet:

What’s the real‑world kWh/100 km at 100-110 km/h with climate control on?
Does it have a heat pump and battery pre‑conditioning?
What tyre size/type ships as standard? Any low‑rolling‑resistance option?
What’s the usable battery capacity, not just the gross figure?

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How do I put this into action and avoid regret?

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Follow these steps, then test-drive with purpose.

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\n Get the three numbers that matter\n
- Usable battery (kWh), not just gross.
- Real‑world kWh/100 km at your speeds (aim to find owner logs or independent tests).
- Your $/kWh at home and typical DC price you’d pay.
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\n Do the simple calculations\n
- Range (km) = usable kWh ÷ (kWh/100 km) × 100.
- Grid kWh/100 km = (kWh/100 km) ÷ charging efficiency.
- Cost per 100 km = Grid kWh/100 km × $/kWh; cost per km = result ÷ 100.
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\n Translate to your life\n
- Apartment or frequent DC use: Prioritise low kWh/100 km; public fast charging can double or triple per‑km cost versus home.
- Suburban with home L2: You can tolerate a slightly higher kWh/100 km if home power is cheap or solar-fed.
- Long‑distance/rural: Aerodynamics beats battery size at 100-110 km/h. A slippery midsize often travels further per hour of charging than a bluff‑fronted giant.
- Towing or roof boxes: Expect big penalties. Budget 30-60% more kWh/100 km when loaded or towing at speed.
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\n Pre‑empt common objections\n
- “I’ll just buy the biggest battery.” Heavier packs raise consumption, price, and charge time. Efficiency still wins on cost and convenience.
- “WLTP says it’s fine.” Use WLTP to shortlist, real‑world kWh/100 km to choose.
- “Fast charging is cheap enough.” Pricing can be per kWh, per minute, or mixed with idle fees; your effective $/kWh can jump, especially when charging slows at high state of charge.
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\n Shop and test smart\n
- Ask the dealer to reset the trip computer and do a 30-50 km loop at your real motorway speed with climate control on. Note kWh/100 km.
- Check for a heat pump, battery pre‑conditioning, tyre type, and aero accessories.
- Verify usable battery capacity and charging curve; efficiency plus a stable charging curve equals quicker road trips.
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Quick “use it now” tips to improve your kWh/100 km

Pre‑condition the cabin and battery while plugged in.
Prefer a heat pump if you see winters.
Cruise at the efficient sweet spot (often 90-110 km/h).
Keep tyres at the correct pressure and ditch empty roof racks/boxes.
Use regen/one‑pedal driving in traffic.
Charge mostly at home/work L2; reserve DC for trips.
Avoid frequent 0-100% cycles; moderate state‑of‑charge habits slow degradation.

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Watch the trip computer to see how real driving conditions shift efficiency.

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The shift is simple but powerful: stop shopping by headline range and start by kWh/100 km.

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Efficiency is the lever that determines how far you go, how often you stop, and how much you spend.

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Grab your spec sheet, plug your numbers into the quick formulas above, set a realistic efficiency target for your life, and you’ll pick an EV you’re still happy with years down the road.

kWh/100 km: The EV Number That Matters