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LUT And Flip Flop Count Calculator

Work out lut and flip flop count instantly with clear inputs, formula shown and shareable results.

About LUT And Flip Flop Count Calculator

Gate-count estimates translate to LUTs by dividing by gates per LUT — about 6-10 for a 6-input LUT — and then by a packing efficiency, because synthesis cannot always fill every LUT input. Register count follows from the design's sequential density.

Formula

LUT estimate

LUTs = gates / gates per LUT / packing efficiency; slices = LUTs / LUTs per slice

Worked example

With the default values below, LUT And Flip Flop Count Calculator returns LUTs required of 26,471. Change any input above and every figure here is recalculated in your browser.

Inputs used

Equivalent gate count
180,000 gates
Gates per LUT
8 gates
Registers per LUT
0.8 x
LUT inputs
6 inputs

Results

LUTs required
26,471 LUTs
Flip-flops required
21,177 flops
Slices required
3,309 slices
Assumed packing efficiency
85.0% %

Step by step

  1. 1Values used
  2. 2LUT estimate
  3. 3LUTs required= 26,471 LUTs
  4. 4Flip-flops required= 21,177 flops
  5. 5Slices required= 3,309 slices
  6. 6Assumed packing efficiency= 85.0 %

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 1 decimal place, 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 many gates does a 6-input LUT replace?

It can implement any 6-input function, equivalent to roughly 8-20 gates for complex logic but only 1-2 for simple wide gates. Averages of 6-10 are used for estimating.

Why is packing efficiency below 100%?

Logic partitioning cannot always use all inputs of every LUT, and placement constraints prevent perfect packing into slices.

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LUT And Flip Flop Count Calculator – Calculate LUTs required