Bloom Filter Calculator | Size and Hash Count

Bloom filter calculator for sizing bit arrays: enter item count and target false positive rate to get bits, hash functions and memory. Free. Designed specifically for developers and professionals, this free online calculator runs entirely in your browser to process tasks quickly and securely. Enjoy unlimited usage with no data tracking and no registration required.

Also known as: bloom filter calculator · bloom filter size calculator · bloom filter false positive rate · optimal hash functions bloom filter · bloom filter bits per element · calculate bloom filter memory · bloom filter sizing tool · bloom filter parameter calculator

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Filter Parameters

Expected items (n)

How many distinct elements you will insert. Size for the peak, not today.

Target false positive rate (%)

1 means one in a hundred lookups for an absent key wrongly answers yes.

Hash functions (k), optional

Override when your library fixes k. The achieved rate is recomputed for the value you set.

m = -n ln(p) / (ln 2)²

k = (m / n) ln 2

Memory depends on the item count and the error rate only. The size of each item never enters the formula, so a filter over 10 million 2 KB documents is exactly as large as one over 10 million integers.

Sizing Result

Bit array size, hash count and the memory tradeoff table will appear here.

About Bloom Filter Calculator

Work out how much memory a Bloom filter needs before you build one. Enter the number of items you expect to insert and the false positive rate you can tolerate, and the calculator returns the bit array size, the optimal number of hash functions, the bits required per item and the error rate you actually get once k is rounded to a whole number.

Key Features

Applies the standard sizing formulas m = -n ln(p) / (ln 2)² and k = (m / n) ln 2
Recomputes the achieved false positive rate from the integer k that ships, not the fractional optimum
Reports memory in bits and bytes plus a human readable size, so a result drops straight into a capacity plan
Shows the fraction of bits set once the filter is full, the number that tells you a filter is overloaded
Compares six target rates from 10 percent down to 0.001 percent side by side, so the memory tradeoff is visible
Accepts a fixed k when your library or storage engine does not let you choose it

Use Cases

Size a Redis Bloom filter that keeps duplicate order IDs out of a payments pipeline running in us-east-1
Estimate the RAM an SSTable Bloom filter adds per node before scaling a Cassandra or RocksDB cluster
Decide whether a crawler can hold 50 million seen URLs in memory instead of paying for a round trip to a database
Justify a memory budget in a design review by showing what 1 percent versus 0.01 percent actually costs
Check whether an existing filter is undersized by comparing its real item count against the rate it was built for
Pick a bits-per-item target when configuring a CDN or proxy cache that exposes the setting directly

Supported Formats

Item counts from 1 to billions

False positive rates from just above 0 to just under 100 percent

Optional fixed hash function count

Related Keywords

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bloom filter parameter calculator

How much memory does a Bloom filter need per item?

At the optimal number of hash functions a Bloom filter needs about 9.6 bits per item for a 1 percent false positive rate, 14.4 bits for 0.1 percent and 19.2 bits for 0.01 percent. Each additional factor of ten in accuracy costs roughly 4.8 more bits per item, which is why very low error rates get expensive quickly. The item size is irrelevant: the filter stores hash positions, not the values, so one million 4 KB documents and one million integers need exactly the same bit array.

Calculated in your browser

Every figure is computed locally in JavaScript. Nothing about your data volumes or capacity plans is sent anywhere.

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Frequently asked questions

What is Bloom Filter Calculator used for?

Bloom filter calculator for sizing bit arrays: enter item count and target false positive rate to get bits, hash functions and memory. Free.

Is Bloom Filter Calculator free to use?

Yes. Bloom Filter Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use Bloom Filter Calculator?

No. Bloom Filter Calculator works immediately in your browser with no signup, login, or email address required.

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