Dehumidifier Size Calculator
This free dehumidifier size calculator sizes the unit from the AHAM area-by-dampness method — the same square-footage-times-dampness logic the manufacturers publish — and then does the one thing most sizing charts skip: it converts to the current label. Since June 2019 the DOE tests dehumidifiers at 65°F instead of 80°F, so a machine that removed 70 pints a day on the old test now measures about 50 on the new one. The charts all over the internet still quote the old, higher numbers, so a shopper reading an old chart against a new box consistently buys a unit that is too small. This calculator shows both scales side by side and tells you the current-label size to actually buy.
It also adjusts for the things that change the real load. An unfinished basement or crawlspace with bare concrete or a dirt floor wicks ground moisture continuously and needs a bigger unit plus a sealed vapor barrier. A washer and dryer in the space add a steady moisture load. A tall ceiling holds more air. And a large or multi-room area is often better served by a whole-house ducted dehumidifier that drains automatically than by a big portable you have to empty. The calculator folds all of that into the recommendation.
One honest caveat it will tell you: a dehumidifier manages humidity, it does not stop water. If you have standing water, beads of moisture, or active seepage, that is a drainage problem to fix at the source — grading, gutters, a French drain, or a sump pump — before a dehumidifier will ever keep up. Aim for 30 to 50 percent relative humidity per the EPA and CDC. No pricing, no signup — just the pint capacity and the size to buy. It is part of a growing HVAC and ventilation section.
Dehumidifier Size Calculator
What size dehumidifier do you need? Enter your space and how damp it is and this calculator returns the pints-per-day capacity — on both the current DOE label and the old pre-2019 chart, because a 2019 test-procedure change dropped ratings about 30% and most sizing charts online still quote the old numbers. Size from the wrong scale and you buy one too small. Free, no signup.
Space
Dehumidifier capacity is sized by the area and how damp it is. An unfinished concrete or crawlspace wicks moisture and needs more.
How damp is it?
Pick the description that matches. Standing water or seepage is a drainage problem — fix the water source first.
Calculation Formulas
The AHAM-style chart scales capacity by area and dampness. Moderately damp ≈ 6 + 0.008 × area; wet ≈ 10 + 0.016 × area (pints/day on the pre-2019 scale).
Example:
1,000 sq ft moderately damp → 6 + 0.008 × 1000 = 14 pints/day (old scale).
In June 2019 the DOE test condition dropped from 80°F to 65°F, so measured capacity fell about 30%. The same machine that was labeled 70-pint is now labeled about 50-pint.
Example:
14 pints/day (old) × 0.71 ≈ 10 pints/day on the current label.
A washer/dryer in the space adds a steady moisture load; add roughly 5 pints/day (old scale) before the re-rating.
Example:
14 + 5 = 19 pints/day (old scale) with laundry.
Capacity is charted for ~8-ft ceilings; a taller room holds more air and moisture, so add about 25%.
Example:
14 × 1.25 = 17.5 pints/day for a 10-ft ceiling.
Bare concrete and dirt floors wick ground moisture continuously, so size up and add a vapor barrier — otherwise the unit runs endlessly.
Example:
14 × 1.2 ≈ 17 pints/day over unsealed concrete.
Round the current-scale requirement up to a standard purchasable size (20, 30, 35, or 50 pint on the 2019 label).
Example:
10 pints/day → a 20-pint (current-label) unit.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| DOE re-rating factor | × 0.71 | Old 80°F rating to new 65°F (2019+) label. |
| Moderately damp | 6 + 0.008·A | Old-scale pints/day: musty smell in humid weather. |
| Wet | 10 + 0.016·A | Old-scale pints/day: beads of moisture / seepage. |
| Laundry add | +5 pints | Extra moisture load from a washer/dryer. |
| Tall ceiling | × 1.25 | Adjustment for ceilings 10 ft and higher. |
| Concrete/crawlspace | × 1.2 | Ground-moisture wicking from unsealed floors. |
| Target humidity | 30–50% RH | EPA/CDC recommended indoor relative humidity. |
| Standard sizes | 20/30/35/50 pt | Common current-label capacities (2019 scale). |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
AHAM DH-1 — Dehumidifier Sizing(AHAM DH-1)
View StandardThe Association of Home Appliance Manufacturers standard that defines dehumidifier capacity testing and the area-by-dampness sizing chart.
Key Requirements:
- •Capacity rated in pints of water removed per 24 hours.
- •Sizing scales with area and dampness level.
- •Latest edition is DH-1-2022.
DOE 10 CFR 430 — Test Procedure (2019)(10 CFR 430)
View StandardThe federal test procedure whose June-2019 revision changed the rating condition from 80°F to 65°F, dropping labeled capacity about 30%.
Key Requirements:
- •Capacity tested at 65°F / 60% RH (was 80°F).
- •Old ratings map to new labels at roughly ×0.71.
- •Integrated Energy Factor (IEF) reported for efficiency.
ENERGY STAR — Dehumidifiers(ENERGY STAR)
View StandardCertifies efficient dehumidifiers by Integrated Energy Factor, useful for units that run for months at a time.
Key Requirements:
- •Minimum IEF (liters per kWh) by capacity class.
- •Whole-home/ducted units have their own criteria.
- •Look for it on units that run continuously.
EPA / CDC — Indoor Humidity(EPA IAQ)
View StandardPublic-health guidance to keep indoor relative humidity between 30% and 50% to limit mold, dust mites, and other allergens.
Key Requirements:
- •Keep relative humidity at 30–50%.
- •Below ~60% RH discourages mold growth.
- •Fix bulk-water intrusion at the source, not with a dehumidifier.
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
The 2019 Label Change
Old chart vs. new label
Because the DOE test moved from 80°F to 65°F in June 2019, an old "70-pint" unit is now labeled about "50-pint." Sizing charts across the web still quote the old numbers, so a shopper reading an old chart against a new box buys one too small.
Regional Examples:
Space Type & Ground Moisture
Concrete and crawlspaces
A finished living space dries out and stays dry; an unfinished basement or crawlspace with bare concrete or a dirt floor wicks ground moisture nonstop. Those spaces need a larger unit and a sealed vapor barrier, or the dehumidifier never catches up.
Regional Examples:
Climate
Humid regions need more
Gulf Coast, Southeast, and other humid climates carry a much higher outdoor dew point, so the same space needs more dehumidification than it would in an arid region. Cold spaces below about 65°F favor a desiccant unit over a refrigerant one, which frosts up.
Regional Examples:
Portable vs. Whole-House
Coverage and drainage
A portable unit handles one room or a small basement and needs its bucket emptied unless you run a drain hose. For a large or multi-room area, a whole-house ducted dehumidifier tied into the HVAC dries every room evenly and drains automatically.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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How to Use This Calculator
- Enter the area you want to dehumidify in square feet, and pick the space type — living space, finished basement, or unfinished concrete/crawlspace.
- Set the ceiling height (tall ceilings need more) and whether there is a washer/dryer in the space.
- Choose the dampness level that matches — from a musty smell in humid weather up to beads of moisture or seepage on the floor.
- Click Calculate to get the recommended size on the current DOE label, plus your need on both the new and old (pre-2019) scales.
- Buy a unit at or above the current-label size; add a vapor barrier for unsealed concrete and a drain hose for continuous operation.
- If the dampness is "wet," fix the water source first — a dehumidifier will not keep up with active water intrusion.
The 2019 rating change — why old charts buy you the wrong size
Dehumidifier capacity is the pints of water the unit pulls from the air in 24 hours, and it is sized by area and dampness. The complication is the label. Before June 2019, the DOE tested dehumidifiers at 80°F; after that date the test condition dropped to 65°F, which is closer to a real basement, and measured capacity fell roughly 30 percent as a result. Nothing about the machines changed — only the number on the box. So a unit that was sold as a 70-pint before 2019 is the same machine now sold as about a 50-pint, and a 50-pint became about a 30-pint. Almost every sizing chart and rule of thumb online still uses the old, higher numbers, which means if you read an old chart and buy a box with that number, you get a unit that is one size too small. This calculator computes your need and shows it on both scales so you can buy correctly. It sizes the unit only; it does not pick a specific model or design a drainage system, and it is guidance rather than code. Remember that a dehumidifier controls humidity, not bulk water — fix any seepage at the source first, and target 30 to 50 percent relative humidity.
Frequently Asked Questions
What size dehumidifier do I need?
Size it by area and dampness. On the current DOE label, a moderately damp 1,000-square-foot basement needs about a 20-pint unit; a very damp or larger space climbs to 30, 35, or 50 pints. The important twist is the label change: since June 2019 dehumidifiers are tested at 65°F instead of 80°F, so ratings fell about 30 percent. If you read an old chart that says '50-pint' and buy a new box labeled 50-pint, you've actually bought one size too small — this calculator shows both scales so you don't.
Why did dehumidifier pint ratings change in 2019?
In June 2019 the Department of Energy changed the test condition for dehumidifiers from 80°F to 65°F, which is closer to a real basement temperature. Because a dehumidifier removes less water from cooler air, the measured capacity of the exact same machine dropped roughly 30 percent. Nothing about the units changed — only the number on the label. So an old 70-pint became about a 50-pint, and an old 50-pint became about a 30-pint. Sizing charts across the web still quote the old numbers, which is why so many people accidentally buy a unit that's too small.
What size dehumidifier for a basement?
For a typical 1,000-square-foot basement that's damp with an occasional musty smell, a 30-pint (current-label) unit is a good starting point; a very damp basement or one with a laundry area moves up to 35 or 50 pints. Two basement-specific factors push the size up: unfinished concrete and dirt floors wick ground moisture continuously, so add capacity and a sealed vapor barrier, and cool basements below about 65°F favor a desiccant unit over a refrigerant one that frosts up. A drain hose to a floor drain or sump lets it run unattended.
Will a dehumidifier fix a wet basement?
No — and this is the most important thing to get right. A dehumidifier removes moisture from the air; it does nothing about liquid water coming through walls or floors. If you have standing water, beads of moisture on the concrete, or active seepage, that's a drainage problem to fix at the source: regrade the soil away from the foundation, extend downspouts, add a French drain, or install a sump pump. Once the bulk water is controlled, a properly sized dehumidifier keeps the remaining humidity in the healthy 30 to 50 percent range. Running one against active seepage just wastes electricity.
How many pints per square foot for a dehumidifier?
There's no single 'pints per square foot' number because dampness matters as much as area — a musty 1,000-square-foot room and a seeping 1,000-square-foot room need very different units. The AHAM method uses a base plus a per-square-foot rate that rises with dampness: roughly 6 + 0.008 per square foot for moderately damp up to 10 + 0.016 for wet, on the old scale, then converted to the current 2019 label. That's why this calculator asks for the dampness level and space type rather than just square footage, and why a flat 'pints per square foot' shortcut usually misleads.
Should I get a whole-house or portable dehumidifier?
It depends on the area and how hands-off you want it. A portable unit handles one room or a small basement well and is inexpensive, but you either empty its bucket regularly or run a drain hose. For a large space (roughly over 1,500 square feet), a multi-room area, or a whole-home humidity problem, a whole-house dehumidifier ducted into the HVAC system dries every room evenly, drains automatically to a condensate line, and runs quietly out of sight. It costs more upfront but is the better answer for big or persistent moisture loads.