Warm just yourself
for about 0.7 yen an hour.
An electric lap blanket
is just right.
The short version…
- On medium it costs about 0.7 yen an hour (rated 55 W, but it throttles down once warm)
- Turn the air conditioner down 1°C and you still come out ahead after paying for the blanket
- Leave it on HIGH and lower the air con only 1°C, and you lose a little
Net savings calculator
A lap blanket only saves money if it lets you turn the air conditioner down. The blanket uses some electricity too, so we subtract it from what the air conditioner saves.
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How we calculate: the blanket uses the hourly figures for Koden CWN142H-NC (55 W, 140×82 cm): about 43 / 23 / 4 Wh on high / medium / low. The air conditioner uses the Agency for Natural Resources and Energy figure (2.2 kW unit, 6°C outside, 9 hours a day: 53.08 kWh per winter for each 1°C lower), scaled by degrees and hours. "Winter" is the same estimate's heating season of 169 days. Real results depend on insulation, weather and your air conditioner. At 31 yen/kWh (guideline unit price of Japan's National Fair Trade Council of Household Electric Appliances, revised July 2022).
So on medium even 1°C pays off; on high you need 2°C. Switch down to medium once you're warm.
Our picks by type
- 140×82 cm — covers knees to toes
- About 0.7 yen an hour on medium (55 W, Koden CWN142H)
- Surface about 40°C on high, 32°C on medium
- Hooded, so you can wear it (about 140×80 cm)
- Room-temperature sensor, turns off after 8 hours
- Fully washable (Koden CWH141G)
* Products and prices load from Rakuten Ichiba when you open this page. Search in Japanese: 電気ひざ掛け.
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Who it suits — and who it doesn't
○ Good fit
- You sit at a desk or on the sofa for long stretches
- You're often alone, so heating the whole room feels wasteful
- You'd rather not turn the air conditioner up
- You want to warm just your own legs at work
× Not a good fit
- You move around the house a lot
- You want the room itself to be warm
- You want something for sleeping (use an electric blanket)
- A cord at your feet bothers you
Why "55 W" costs so little
The "55 W" on the box is the maximum, used right after you switch it on. Once it's warm it cuts back, so it uses much less over an hour. It warms your body directly instead of the room's air, so it needs far less electricity than a heater.
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For running costs, use the hourly energy figure (Wh, 1時間あたりの消費電力量), not the rated power (W, 消費電力). If a product doesn't publish it, calculating with the maximum watts will overestimate the cost.
5 tips for choosing
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Size: about 140 cm to cover your feet
From the same maker, the 130 size (40 W) uses about 17 Wh an hour on medium and the 140 size (55 W) about 23 Wh.Size Best for About 130 cm Over your lap; little room under the desk About 140 cm Knees to toes, or over your shoulders -
Shape: flat for sitting, hooded or buttoned for moving
If you want to stand up with it over your shoulders, a hood or buttons keep it from slipping off. -
Does it list hourly energy use?
Some makers publish the hourly figure (Wh) for each setting. With it, you can estimate the cost accurately. -
Auto-off and room sensor
An auto-off timer is reassuring if you walk away and forget it. Some models also adjust to the room temperature. -
Washability
It touches your skin, so check whether the controller detaches and the blanket can be washed. Machine or hand wash depends on the product.
Watch out for low-temperature burns
Warmth just above body temperature can cause a low-temperature burn if it stays on the same spot for a long time. NITE (Japan's product safety agency) says this can happen in 3–4 hours at 44°C, 30–60 minutes at 46°C and 2–3 minutes at 50°C.
Instead: switch to medium or low once warm. The CWN142H-NC surface is about 40°C on high and 32°C on medium (Koden)
Instead: turn it off when you get sleepy, and choose a model with auto-off
Instead: route the cord where it won't be stepped on or pinched. Stop using it if the cord is damaged
Good to know if you live in Japan
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Buy one made for Japan (100V)
Japan's household power is 100V. An electric blanket built for 220–240V countries won't work properly here, and adapters don't fix that. Choose a model sold in Japan. -
Look for the PSE mark
Electric blankets are covered by Japan's Electrical Appliances and Materials Safety Act. Products sold in Japan must carry the PSE mark — be careful with very cheap imports from marketplaces. -
Manuals are usually in Japanese
Many makers post their manuals as PDFs on their websites. A camera-translation app works well for the safety page and the controller (強 high / 中 medium / 弱 low). -
Shopping in English
Amazon.co.jp can be switched to English in the language settings. Product titles are often still in Japanese — search for 電気ひざ掛け or the model number to find more options. -
Your price per kWh may differ
We calculate with 31 yen/kWh, the guideline price used in Japanese catalogs. Your actual price depends on your power company and plan — check your monthly bill (検針票 / your company's app).
FAQ
How much is it per month?
What's the difference from an electric blanket?
What if I turn the air con off and use only the blanket?
Still not sure?
Answer 6 questions to find the heater that's just right for you.