Clock Tree Power Calculator

Work out clock tree power instantly with clear inputs, formula shown and shareable results.

About Clock Tree Power Calculator

Clock power is C V squared f with an activity factor of one, because the clock switches every cycle by definition. That makes the clock tree typically 20-40% of total dynamic power in a synchronous design, and it is why clock gating is the single most effective power optimisation available.

Formula

Clock power

P = C V^2 f, with alpha = 1 since the clock always toggles

Worked example

With the default values below, Clock Tree Power Calculator returns Clock tree power of 1.77. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total clock tree capacitance: 850 pF
Supply voltage: 0.9 V
Clock frequency: 1.8 GHz
Buffer internal power share: 30 %

Results

Clock tree power: 1.77 W
Switching power: 1.24 W
Buffer internal power: 0.53 W
Energy per cycle: 983.57 pJ

Step by step

1Values used
2Clock power
3Clock tree power= 1.77 W
4Switching power= 1.24 W
5Buffer internal power= 0.53 W
6Energy per cycle= 983.57 pJ

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 or fees or charges 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 clock such a large share of power?

Every other net has an activity factor well below one; the clock's is exactly one and it reaches every sequential element on the die.

How much does clock gating save?

Typically 20-40% of total dynamic power, since most registers are idle most cycles. It is standard practice in all modern synthesis flows.