💧What size dehumidifier does this space need?

✓ Tested & verified Updated: Aug 8, 2026 How we calculate this

Dehumidifier size calculator

Floor area (sq ft)

How damp is it

20 pints/day

Chart figure for 800 sq ft at this dampness.

Floor area: 800 sq ft

Rated capacity is measured at 65 °F since 2019. A unit from before that change is rated roughly 30% higher for the same machine — do not compare the two.

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What size dehumidifier do you need?

Cross the floor area with how damp the space actually is. An 800 sq ft basement that smells musty in humid weather takes a 20-pint unit on today’s scale; the same basement with damp patches on the walls takes 25, and one with water seeping in after rain takes 30.

Dampness moves the answer as much as doubling the area does, which is why every honest chart has two axes. The four descriptions used everywhere are worth matching honestly: damp is a musty smell in humid weather, very damp is clammy air and damp patches, wet is beading walls or seepage.

Check which scale a chart is on before trusting it. In 2019 the US Department of Energy moved the test temperature from 80 °F to 65 °F. Less moisture condenses out of cooler air, so the same machine now measures about 30% lower. A 70-pint unit from 2016 and a 50-pint unit today are close to the same appliance — and any chart that still recommends 70 pints for an average basement is quietly a third too big.

This is the whole chart, on today’s scale. Find the row for your area and the column for how the space honestly feels, not how you would like it to feel.

Floor area	Damp	Very damp	Wet
up to 500 sq ft	20 pints	20 pints	25 pints
up to 1,000 sq ft	20 pints	25 pints	30 pints
up to 1,500 sq ft	25 pints	30 pints	40 pints
up to 2,000 sq ft	30 pints	35 pints	45 pints
up to 2,500 sq ft	35 pints	40 pints	50 pints
over 2,500 sq ft	45 pints	50 pints	70 pints

Damp means a musty smell in humid weather. Very damp means the air feels clammy and there are damp patches. Wet means beading walls, seepage after rain or standing water — and at that point the dehumidifier is managing a symptom while the drainage or the damp-proofing is the actual repair.

Frequently asked questions

What size dehumidifier for a 1,000 sq ft basement?

Twenty pints on the current scale if it is only damp, 25 if it is very damp, and 30 if there is visible seepage. Older charts will tell you 50 or 70 for the same room — those figures are on the pre-2019 scale and would be roughly 35 and 50 today.

Why did dehumidifier pint ratings change in 2019?

The Department of Energy revised the test procedure so that units are measured at 65 °F rather than 80 °F. Cooler air holds less moisture, so the same machine condenses less water during the test and its published capacity dropped by roughly 30%. Nothing about the hardware changed — only the number on the box, and the older number was flattering for basements, which are cool.

Is a bigger dehumidifier always better?

Not usefully. A larger unit reaches the target humidity faster and then cycles, which costs more to buy and more to run than a right-sized one held at a steady setpoint. Where extra capacity does pay is a cool basement, since capacity falls as temperature drops — a unit rated at 65 °F delivers noticeably less at 50 °F.

What humidity should I set it to?

Between 45 and 50% relative humidity in a living space. Below 40% is unnecessary and dries out timber and joinery; above 60% is where mould, dust mites and that basement smell start. A cheap hygrometer somewhere away from the unit is worth more than the setting on the dial, which reads its own outlet air.

Does the whole house count, or just the room?

Whatever the air moves freely through. A basement with an open stairwell is connected to the floor above and will pull moisture down from it, so size for the basement and expect the unit to run longer. Closed rooms off the same basement need their own airflow or their own unit.

Will a dehumidifier heat the room?

Yes, slightly — everything it takes in electricity comes back as heat, plus the latent heat released as water vapour condenses. In summer that is unwelcome in a living room and irrelevant in a basement. In winter it is a small bonus that makes a cool basement fractionally easier to dehumidify.

How we calculate this

Sizing uses a floor-area by dampness chart on the post-2019 US Department of Energy rating scale, where capacity is measured at 65 °F rather than the earlier 80 °F. The dampness columns follow the standard descriptions — damp (musty in humid weather), very damp (damp patches, clammy air) and wet (beading walls or seepage) — and rows run in 500 sq ft steps to 2,500 sq ft. Because the answer comes from a published chart rather than a rate per square foot, the tool reports the chart value directly rather than rounding to a size ladder. Capacity falls as the room gets colder; a unit used in a space held below about 60 °F will deliver less than its rating.

Worked example

With Floor area (sq ft) 800, How damp is it Damp — musty smell in humid weather, this page works out 20 pints/day. Chart figure for 800 sq ft at this dampness.

Floor area800 sq ft

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