How this calculator works
A dehumidifier is sold by how many pints of water it removes from the air in 24 hours. The amount you need depends on the size of the space and how much moisture is coming into it. The standard sizing chart gives four levels of dampness, and each one rises in a straight line with floor area: more floor means more moisture to remove.
The base and step are 10 and 4 for a moderately damp space, 12 and 5 for very damp, 14 and 6 for wet and 16 and 7 for extremely wet. A taller ceiling means more air, so a ceiling over 8 ft scales the answer up in proportion.
Worked example: a 1,000 ft² basement that feels damp in humid weather needs 10 + 4 × (1,000 − 500) ÷ 500 = 14 pints per day on the older rating. The 2019 test conditions are less generous, so the same job shows as about 14 × 0.7 = 10 pints on a current label. Machines are sold in set sizes, so pick the next size up.
Pints per day (older rating) by area and dampness, 8 ft ceilings
Multiply by about 0.7 for the number on a current label.
| Floor area | Moderately damp | Very damp | Wet | Extremely wet |
|---|---|---|---|---|
| 500 ft² | 10 | 12 | 14 | 16 |
| 1,000 ft² | 14 | 17 | 20 | 23 |
| 1,500 ft² | 18 | 22 | 26 | 30 |
| 2,000 ft² | 22 | 27 | 32 | 37 |
| 2,500 ft² | 26 | 32 | 38 | 44 |
Tips before you buy
- If you are between two sizes, buy the larger one. A dehumidifier that is too small runs all day and never reaches the target, while a bigger one reaches it, then rests.
- Aim for 30 to 50% relative humidity, and under 60% always. A cheap hygrometer tells you what the room is actually doing.
- A unit with a built-in pump or a drain hose connection saves emptying the bucket, which matters in a basement where it runs for days.
- Fix the cause as well. Gutters and downspouts that send water away from the foundation, a sealed dryer vent and a vapor barrier on a crawl space remove moisture the dehumidifier would otherwise have to handle.
- Dehumidifiers work poorly in cold rooms: below about 60°F the coils frost up. For a cold basement, a model rated for low temperatures is worth the extra cost.
- Set the humidity target, then check the water filter and coils every month or so to keep it running efficiently.
Tools & materials for this project
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Frequently asked questions
What size dehumidifier do I need for a 1,000 square foot basement?
About 14 pints per day on the older rating if it is only moderately damp, 17 if it is very damp, and 20 if it is wet. On a current label these are about 10, 12 and 14 pints. Machines are sold in set sizes, so choose the next size up.
What size dehumidifier do I need for a 2,500 square foot house?
A moderately damp space of 2,500 ft² needs about 26 pints per day on the older rating, and an extremely wet one 44. On a current label that is about 19 to 31 pints. Larger models, around 50 to 70 pints, are common for big basements.
What changed with dehumidifier ratings in 2019?
The US Department of Energy moved the test from 80°F and 60% humidity to a cooler 65°F, which is closer to a real basement. The same machine is now rated about 30% fewer pints, so a 50-pint unit from before is a 35-pint unit today.
Is it OK to buy a bigger dehumidifier than I need?
Yes. A larger unit reaches the target humidity sooner and then switches off, so it does not run all day. Compare the energy efficiency (liters per kWh) on the Energy Star label, because bigger is not always less efficient per pint removed.
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