Moth Protection Calculator
Cedar and lavender quantities for natural moth protection.
About this calculator
Cedar wards off clothes moths (Tineola bisselliella) through the thujaplicin oil it releases, and how well it works depends on how much cedar surface area is exposed relative to the enclosed air volume it needs to protect — this calculator uses the industry rule of about 50 cm² of cedar surface per cubic foot of storage as its baseline. It scales that requirement up for two real factors: more vulnerable garments (wool, silk, cashmere, fur — the animal fibers moths actually eat) mean more food source to guard, so garment count adds up to a 30% surface-area penalty; and better ventilation disperses cedar's protective oils faster, so an open rack needs 1.5x the cedar surface of a sealed container, while a sealed bag needs only 0.8x. From the required surface area, it works out how many standard cedar blocks (~100 cm² each) or cedar hangers (~200 cm² each, which double as garment supports) you'd need, and separately recommends lavender sachets as backup protection via linalool, at roughly one sachet per 2 cubic feet scaled by the same ventilation and garment factors.
Because cedar's oils deplete over time, it also converts your chosen refresh interval into an effective schedule adjusted for ventilation (sealed storage holds oils longer, so refreshes are less frequent) and estimates upfront and annual maintenance costs from flat per-unit price assumptions (cedar blocks $1.50, hangers $4, sachets $2, sanding supplies $3/session). None of this replaces mothballs or professional pest treatment for an active infestation — it's a preventive-maintenance plan for garments that are currently moth-free.
Inputs
Results
Cedar blocks needed
11
How to Use This Calculator
- Enter Storage volume (cu ft), Vulnerable garments, and Ventilation level.
- Set Cedar refresh interval (months).
- Review the Cedar blocks needed result.
- Use Cedar hangers recommended and Lavender sachets needed to inform your decision.
How the result changes with Storage volume (cu ft)
| Storage volume (cu ft) | Cedar blocks needed |
|---|---|
| 10 | 6 |
| 15 | 8 |
| 30 | 16 |
| 50 | 27 |
What each input means
- Storage volume (cu ft)
- Total enclosed storage volume in cubic feet. A standard closet is ~20-40 cu ft.
- Vulnerable garments
- Number of wool, silk, cashmere, or fur items stored. Moths target animal fibers.
- Ventilation level
- 0=Sealed container/bag, 1=Closet with door, 2=Open rack/shelf.
- Cedar refresh interval (months)
- How often you plan to sand cedar to refresh the oils. 6 months is typical.
What each result means
- Cedar blocks needed
- Number of standard cedar blocks (approx 4×2 inches each).
- Cedar hangers recommended
- Cedar hangers that both protect and support garments.
- Lavender sachets needed
- Number of lavender sachets for secondary moth deterrence.
- Cedar refreshes per year
- How many times per year to sand cedar surfaces.
- Initial setup cost ($)
- Estimated one-time cost for cedar blocks, hangers, and lavender.
- Annual maintenance ($)
- Yearly cost for lavender replacement and cedar sanding supplies.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersStorage volume (cu ft) = 20, Vulnerable garments = 10, Ventilation level = 1, Cedar refresh interval (months) = 6 = 4 input(s) provided
- Calculate Cedar blocks neededCedar blocks needed11 = 11
- Calculate Cedar hangers recommendedCedar hangers recommended6 = 6
- Calculate Lavender sachets neededLavender sachets needed11 = 11
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does more ventilation mean I need more cedar, not less?
Cedar's protection comes from thujaplicin oil evaporating into the air around your garments, and better ventilation disperses that oil faster instead of letting it concentrate in an enclosed space. The calculator applies a ventilationMultiplier of 0.8x for a sealed container, 1.0x for a closet with a door, and 1.5x for an open rack — so an open rack needs nearly twice the cedar surface area of a sealed container to maintain the same effective concentration of repellent oil.
How does the number of vulnerable garments change the cedar and lavender quantities?
More wool, silk, cashmere, or fur garments mean more food source for clothes moths, so the calculator applies a garmentAttractionFactor that adds up to a 30% surface-area penalty as vulnerable garment count rises (calculated as 1 plus garment count divided by 50, times 0.3). That factor multiplies into both the required cedar surface area and the lavender sachet count, so doubling your vulnerable garments doesn't double the recommendation, but it does meaningfully increase it.
Why does the cedar refresh schedule change with ventilation level, not just the interval I entered?
Your entered refresh interval represents how often you're willing to sand the cedar, but the calculator divides that by the same ventilationMultiplier to get an effective schedule — since open, well-ventilated storage disperses cedar oils faster, it needs sanding more often than the interval you entered to actually keep protection at the intended level. A sealed container, by contrast, holds its oils longer, so its effective refresh interval stays closer to what you entered.
Will this stop an infestation I already have?
No. Cedar and lavender are repellents, not insecticides — they discourage adult moths from choosing a spot to lay eggs, but neither reliably kills eggs, larvae, or the casings already in your fibres, and larvae are the stage that actually eats wool. Quantities sized here are a preventive measure for garments you believe are clean. If you are already seeing holes, shed casings, or small crawling larvae, treat the garments first — laundering, dry cleaning, or 72 hours at freezer temperature all kill the larval stage — and clean the storage space before putting anything back. Adding cedar to an active infestation mostly just gives you cedar-scented moths.
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