Firmware Memory Usage Calculator

Work out firmware memory usage instantly with clear inputs, formula shown and shareable results.

About Firmware Memory Usage Calculator

Flash headroom matters for future features and for over-the-air updates, which typically need room for two images. RAM headroom is more critical still: what remains after static allocation must cover the deepest call stack plus any heap, and running out corrupts memory silently.

Formula

Memory budget

free = size - used; OTA-capable designs need code size below half the flash

Worked example

With the default values below, Firmware Memory Usage Calculator returns Flash remaining of 108.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Flash size: 256 kB
Code and constants: 148 kB
RAM size: 64 kB
Static RAM used: 38 kB

Results

Flash remaining: 108.00 kB
Flash used: 57.81% %
RAM remaining for stack and heap: 26.00 kB
RAM used: 59.38% %

Step by step

1Values used
2Memory budget
3Flash remaining= 108.00 kB
4Flash used= 57.81 %
5RAM remaining for stack and heap= 26.00 kB
6RAM used= 59.38 %

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

How much RAM headroom is safe?

Enough for worst-case stack depth including interrupt nesting, plus heap fragmentation margin. 25-30% free static RAM is a common rule.

Why does OTA need half the flash?

A dual-bank scheme keeps the running image while writing the new one, so the largest image can only be just under half the available flash.