Dehumidifier Size Calculator
Short answer: dehumidifier sizing starts at 10 pints/day for the first 500 sq ft, plus 4 pints/day per additional 500 sq ft, then a dampness adjustment for how wet the space feels. A damp 500 sq ft room lands at a 20-pint nameplate unit; a very wet 2,000 sq ft basement needs a 50-pint unit with continuous drainage. This free calculator runs that math and tells you whether a unit you’re considering is sized right, undersized, or oversized.
Find the right dehumidifier capacity for your space, or check whether a unit you're considering is big enough. This is a vendor-neutral estimate — the base sizing rule comes from ENERGY STAR and Home Depot guidance, the dampness adjustment is our own and clearly labeled, and we never inflate the number to sell a bigger unit.
How the calculator works
It starts from the standard ENERGY STAR / Home Depot base rule, then applies a dampness adjustment:
| Step | What it does |
|---|---|
| Base load | 10 pints/day for the first 500 sq ft, + 4 pints/day for each additional 500 sq ft |
| Dampness | Damp ×1.0, Very Damp ×1.2, Wet ×1.4, Very Wet ×1.6 (our disclosed adjustment) |
| Space type | Basement or crawl space is treated as at least Very Damp (×1.2 minimum) and gets a continuous-drainage recommendation |
| Required load | base × dampness, rounded up to whole pints/day |
| Recommended size | the nearest common nameplate at or above the required load, from 20 / 30 / 35 / 50 pint |
The exact formula: base = 10 + ceil(max(0, sqft − 500) ÷ 500) × 4, then required = ceil(base × dampMultiplier). If the required load is above 50 pints, we recommend a 50-pint unit plus a second unit, or a dedicated crawlspace/commercial dehumidifier.
The mistake to avoid: undersizing a wet space
With dehumidifiers, the costly error is going too small. A unit that's undersized for a wet basement runs around the clock, never reaches your target humidity, and burns out its compressor years early. A modestly oversized unit, by contrast, hits the setpoint and then cycles — quieter and longer-lived. When you're between two sizes for a damp or wet space, size up. The 2020 label change makes this trap worse, because a unit that looks like a big 70-pint machine on an old box is really a 50-pint unit by today's rating — see our pint sizes explained guide.
Frequently asked questions
What size dehumidifier do I need for 500 square feet?
A damp 500 sq ft space has a 10 pint/day base load, so a 20-pint unit (2020 scale) is the starting size. Very damp or wet steps you up toward 30 pints and continuous drainage.
What size dehumidifier for a 1,000 sq ft basement?
Basements are treated as at least Very Damp. A 1,000 sq ft basement is a ~14 pint base, ~17 pints after the adjustment — a 20-pint unit with continuous drainage. A wet basement pushes toward 30 pints. See best dehumidifier for a basement.
Is a bigger dehumidifier always better?
No. Right-sized or modestly oversized is ideal; wildly oversized wastes money and can over-dry a small room. Undersizing is the worse mistake — it runs nonstop and wears out.
What does the 2020 pint rating change mean?
DOE moved the capacity test from 80°F to 65°F in 2020, so the same machine now shows a lower pint number (an old "70-pint" is today's ~50-pint). Size using the current number. Full explanation here.
Related: What size dehumidifier do I need? (full guide) · Dehumidifier pint sizes explained · Best for a basement
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