Lazy Load Benefit Calculator

Work out lazy load benefit instantly with clear inputs, formula shown and shareable results.

About Lazy Load Benefit Calculator

Lazy loading defers everything below the fold, so the initial payload is only the visible images and the deferred weight is the rest. On a long gallery page lazy loading can cut the initial payload by 85%, and images above the fold should be excluded so they are not delayed.

Formulas

Initial payload

initial KB = images above the fold x average image weight

Deferred

deferred = (total images - above the fold) x average weight

Worked example

With the default values below, Lazy Load Benefit Calculator returns Weight deferred by lazy loading of 4,080.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Images on the pageminimum 1: 40
Images visible without scrollingminimum 0: 6
Average image weightminimum 0.1 KB: 120 KB

Results

Weight deferred by lazy loading: 4,080.0 KB
Weight still loaded up front: 720.0 KB
Share of image weight deferred: 85.00%
Deferred weight in megabytes: 3.984 MB

Step by step

1Values used
2Initial payload
3Deferred
4Weight deferred by lazy loading= 4,080.0 KB
5Weight still loaded up front= 720.0 KB
6Share of image weight deferred= 85.00
7Deferred weight in megabytes= 3.984 MB

Assumptions and limits

The result is derived only from the 3 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 3 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

How is the Lazy Load Benefit figure worked out?

initial KB = images above the fold x average image weight. Lazy loading defers everything below the fold, so the initial payload is only the visible images and the deferred weight is the rest.

Why does this matter?

On a long gallery page lazy loading can cut the initial payload by 85%, and images above the fold should be excluded so they are not delayed.

What do I need to enter?

Enter images on the page, images visible without scrolling, average image weight. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.