Our pick for your room
Best Overall
DREO Space Heater
Best for bedrooms and home offices
- 1500W
- Plugs into a normal outlet
- Warms about 150 sq ft of this room
See today’s price on Amazon
Space heater size calculator: the watts your room needs, shown in 3D
Put in your room’s size, ceiling, insulation and how cold it gets. It works out the watts and BTU the room needs on the coldest days, shows in 3D how far one heater reaches, what it costs to run, and the heaters that cover it.
144 sq ft · 8 ft ceiling · average · 20 to 40°f
One 1,500 W space heater will do it
Your room needs about 1,450 W (4,900 BTU an hour) on the coldest days. One 1,500 W heater, the most a normal outlet allows, covers it.
Try a setup
1 × 1,500 W: Keeps the whole room warm
Need: 1,450 W1 × 1,500 W
Your room
ft
12 ft
ft
12 ft
ft
8 ft
Insulation
A typical home: some insulation, ordinary windows.
Coldest winter days outside
Most of the US on a winter night.
Running cost
¢/kWh
18¢ per kWhUS average is about 18¢
h
8 hours a day
Your room’s numbers
- Floor area
- 144 sq ft (12 ft × 12 ft)
- Heat needed on the coldest days
- 1,450 W = 4,900 BTU/hour
- One 1,500 W heater warms
- About 150 sq ft of this room
- Plug-in heaters needed
- 1
- Cost to run, cold day
- 26¢ an hour · $62.21 a month at 8 h/day
- A 1,500 W heater on high
- 27¢ an hour · $6.48 a day non-stop
A 1,500 W heater draws 12.5 A at 120 V. Plug it straight into a wall outlet (no extension cord or power strip), run one per circuit, and keep 3 ft clear around it.
Space heaters for your room
See all Best Space Heaters: Top 5 on AmazonAlso worth a look
Best Tower
Lasko 23" Ceramic Tower
- 1500W
Best for medium rooms and living areas
See today’s price on Amazon
Quietest
De’Longhi Oil-Filled Radiator
- 1500W
Best for silent, even heat while you sleep
See today’s price on Amazon
Best Budget
Amazon Basics Ceramic Heater
- 1500W / 900W
Best for small rooms on a budget
See today’s price on Amazon
Heating a garage or workshop? See our Best Garage Heaters: Top 5 on Amazon.
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Space heater size chart: watts by room size
For an 8 ft ceiling, average insulation and a cool winter (10 W per sq ft). Drafty rooms, taller ceilings and colder places need more: use the calculator above. 1 W = 3.412 BTU per hour.
| Room size | Watts needed | BTU per hour | What to buy |
|---|---|---|---|
| 50 sq ft | 500 W | 1,700 BTU | One heater on low |
| 100 sq ft | 1,000 W | 3,400 BTU | One 1,500 W heater |
| 150 sq ft | 1,500 W | 5,100 BTU | One 1,500 W heater |
| 200 sq ft | 2,000 W | 6,800 BTU | Two 1,500 W heaters |
| 250 sq ft | 2,500 W | 8,500 BTU | Two 1,500 W heaters |
| 300 sq ft | 3,000 W | 10,200 BTU | Two 1,500 W heaters |
| 400 sq ft | 4,000 W | 13,600 BTU | A 240 V garage heater or propane |
| 500 sq ft | 5,000 W | 17,100 BTU | A 240 V garage heater or propane |
| 600 sq ft | 6,000 W | 20,500 BTU | A 240 V garage heater or propane |
| 800 sq ft | 8,000 W | 27,300 BTU | A 240 V garage heater or propane |
| 1000 sq ft | 10,000 W | 34,100 BTU | A 240 V garage heater or propane |
How the calculator works
10 watts per square foot to start. Heater makers rate a 1,500 W heater for about 150 sq ft, which is 10 W per sq ft for a room with an 8 ft ceiling, average insulation and a cool winter. The calculator starts there and scales by your ceiling height, since a taller room has more air to heat. 1 W of heat is 3.412 BTU per hour.
Your insulation and climate. These are our rule-of-thumb multipliers: a well-insulated room needs about 0.8× the heat, a drafty one 1.3× and a bare garage or shed 1.75×. A place where the coldest days stay above 40°F needs 0.8×, 0 to 20°F needs 1.2× and below 0°F 1.4×. The answer is the heat your room loses on its coldest days, so most of the time a thermostat runs the heater for less.
What a plug can give. 1,500 W is the most a heater can draw from a normal 120 V outlet (12.5 amps). Up to 750 W, one heater on its low setting does it; up to 1,500 W, one heater on high; up to 3,000 W, two heaters on separate circuits. Past that you need a 240 V garage or shop heater put in by an electrician, or a propane heater in a ventilated space.
Running cost. Watts ÷ 1,000 × hours × your price per kWh. We show the cost for the heat your room needs on a cold day and for a 1,500 W heater left on high. The US average is around 18¢ per kWh; your bill shows your rate.
What it can’t know. Sun through windows, how warm you like it, or whether central heating is also running. If the room has another heat source, a smaller heater will top it up.
By Jamilur Rahman. Prices on this page are from our guides and change on Amazon; we earn from qualifying purchases.
Questions people ask
What size space heater do I need?
Plan on about 10 watts per square foot for a room with an 8 ft ceiling and average insulation. A 150 sq ft bedroom needs about 1,500 W, which is one standard space heater. Drafty rooms, taller ceilings and colder places need more; the calculator adds those in.
What size space heater for 400 sq ft?
About 4,000 W (13,600 BTU) with an 8 ft ceiling and average insulation, or 5,200 W if it is drafty. That is more than two plug-in heaters (3,000 W), so use a 240 V heater of 4,000 to 5,000 W, or heat the part of the room you use with two 1,500 W heaters on separate circuits.
What size space heater for 200 square feet?
About 2,000 W in an average room, so two 1,500 W heaters on cold days, or one on high in a well-insulated room (it needs 1,600 W, so one heater covers about 94%). For 300 sq ft you need about 3,000 W: two heaters on separate circuits.
How many watts do I need to heat a garage?
An uninsulated two-car garage (20 × 20 ft, 8 ft ceiling) needs about 7,000 W in a cool climate, so a 7,500 W 240 V garage heater or a 30,000 BTU propane heater. A one-car garage (12 × 22 ft) needs about 4,600 W: a 5,000 W heater. A plug-in 1,500 W heater only warms the spot you stand in.
How much does it cost to run a space heater?
A 1,500 W heater on high uses 1.5 kWh an hour: about 27¢ an hour at 18¢ per kWh, $2.16 for 8 hours, or $6.48 a day if it runs 24/7. With a thermostat it cycles off once the room is warm, so the real cost is usually lower.
How big a room can a 1,500 watt space heater heat?
About 150 sq ft with an 8 ft ceiling and average insulation, about 190 sq ft if the room is well insulated, and about 115 sq ft if it is drafty. Past that it takes the chill off but won’t keep the whole room warm on the coldest days.
How many watts is a space heater on low?
Most 1,500 W space heaters have a low setting of 750 to 900 W, enough for a room of about 75 to 90 sq ft. Small desk heaters run at about 200 to 500 W and warm only you.
How many BTU is a 1,500 watt heater?
About 5,100 BTU per hour (1,500 × 3.412). Every electric heater turns all of its power into heat, so a 1,500 W ceramic, oil-filled or infrared heater gives the same heat; they differ in how fast and how evenly they spread it.
Can you heat a house with space heaters?
Only a room or two. A 1,500 sq ft house needs about 15,000 W, or ten 1,500 W heaters, each on its own circuit. Use space heaters to warm the rooms you are in and turn the central heating down.
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