Build Time Savings From Cache Calculator

Work out build time savings from cache instantly with clear inputs, formula shown and shareable results.

About Build Time Savings From Cache Calculator

Caching turns build time into a weighted average of the warm and cold paths. Because the hit rate multiplies the saving, moving from 60 to 90 percent hit rate matters as much as making the warm path faster. The daily compute hours saved is the figure that converts directly into runner cost or reduced queueing.

Formula

Cached build time

average = hit rate x warm time + (1 - hit rate) x cold time; saving per build = cold - average

Worked example

With the default values below, Build Time Savings From Cache Calculator returns Compute hours saved per day of 16.90. Change any input above and every figure here is recalculated in your browser.

Inputs used

Build time without cacheminimum 1 s: 420 s
Build time with a cache hitminimum 0 s: 95 s
Cache hit rateaccepts 0–100 %: 78 %
Builds per dayminimum 1: 240

Results

Compute hours saved per day: 16.90 h
Average build time with caching: 167 s
Seconds saved per build: 254 s
Reduction in average build time: 60.4%

Step by step

1Values used
2Cached build time
3Compute hours saved per day= 16.90 h
4Average build time with caching= 167 s
5Seconds saved per build= 254 s
6Reduction in average build time= 60.4

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What lowers the cache hit rate?

Cache keys that include volatile content such as timestamps or full lockfile hashes that change on any dependency bump, and per-branch caches that never share with the mainline.

Can caching cause incorrect builds?

Yes, if the key does not capture everything that affects the output. Always include the toolchain version and the dependency manifest hash in the key.