Bitstream Size Calculator
Work out bitstream size instantly with clear inputs, formula shown and shareable results.
About Bitstream Size Calculator
Bitstream size is logic cells times configuration bits per cell — roughly 100-150 bits each once routing, LUT contents and BRAM initialisation are counted. Configuration time is the compressed size divided by the load interface speed, which is why boot time drives the choice of x8 or x16 flash.
Formula
Bitstream
bits = cells x config bits per cell; config time = compressed bits / interface speed
Worked example
With the default values below, Bitstream Size Calculator returns Bitstream size of 2.96. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Logic cells
- 215,000 cells
- Configuration bits per cell
- 110 bits
- Compression ratio
- 1.8 x
- Configuration flash speed
- 100 Mbit/s
Results
- Bitstream size
- 2.96 MB
- Compressed size
- 1.64 MB
- Configuration time
- 131.39 ms
- Total configuration bits
- 23.65 Mbit
Step by step
- 1Values used
- 2Bitstream
- 3Bitstream size= 2.96 MB
- 4Compressed size= 1.64 MB
- 5Configuration time= 131.39 ms
- 6Total configuration bits= 23.65 Mbit
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
Why is the bitstream so much larger than the logic?
Most bits configure routing, not logic. Interconnect multiplexers vastly outnumber LUT configuration bits.
How is configuration time reduced?
Wider and faster flash interfaces, bitstream compression, and partial reconfiguration where only the changed region is loaded.
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