IR Drop In Power Grid Calculator

Work out ir drop in power grid instantly with clear inputs, formula shown and shareable results.

About IR Drop In Power Grid Calculator

Static IR drop is simply current times grid resistance, but at sub-volt supplies the budget is brutal: 5% of 0.85 V is only 42 mV, so 60 A can tolerate no more than about 0.7 milliohms of grid resistance from the pads to the load.

Formula

IR drop

drop = I x R_grid; must stay within the supply tolerance budget along with dynamic droop

Worked example

With the default values below, IR Drop In Power Grid Calculator returns IR drop of 48.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total current: 60 A
Grid resistance to the load: 0.8 mΩ
Nominal supply: 0.85 V
Allowed supply tolerance: 5 %

Results

IR drop: 48.00 mV
Voltage at the load: 0.80200 V
Drop as share of nominal: 5.647% %
Assessment: Exceeds the supply tolerance - strengthen the grid

Step by step

1Values used
2IR drop
3IR drop= 48.00 mV
4Voltage at the load= 0.80200 V
5Drop as share of nominal= 5.647 %
6Assessment= Exceeds the supply tolerance - strengthen the grid

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 compounding frequency into account.
Figures are rounded for display to 5 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 IR drop harder at low voltage?

The absolute tolerance shrinks with the supply while currents rise, so the allowable grid resistance falls quadratically in effect.

How is the grid strengthened?

More and wider metal on upper layers, more power vias, more C4 bumps, and placing high-current blocks near the power entry points.