What is the formal charge formula?

FC = V − N − B/2, where V is the number of valence electrons in the free neutral atom, N is the number of non-bonding (lone pair) electrons on the atom, and B is the total number of bonding electrons around the atom (each bond contributes 2).

How do I count lone pair electrons?

Count the electrons that are NOT involved in any bond. Each lone pair dot pair = 2 electrons. For example, oxygen in water has 2 lone pairs = 4 lone pair electrons.

How do I count bonding electrons?

Count each bond once and multiply by 2 (since each bond is 2 electrons). A single bond = 2, double bond = 4, triple bond = 6. Equivalently, just enter the number of bonds (the calculator divides by 2).

Why does formal charge not equal actual charge?

Formal charge assumes equal sharing of bonding electrons — it is a bookkeeping tool, not a measure of real electron density. Actual partial charges depend on electronegativity differences.

What does a formal charge of zero mean?

It means the atom in the structure has the same number of electrons assigned to it as the free neutral atom — this is the ideal and most stable arrangement.

Formal Charge Calculator

Name: Formal Charge Calculator
Availability: InStock
Author: Nham Vu

Enter an element symbol (or its valence electrons directly), lone pair electrons, and number of bonds to get the formal charge instantly.

Atom Inputs

Element (common)

Valence electrons (V) — free neutral atom

Lone pair electrons (N) — non-bonding

Number of bonds (B/2) — total bonds around atom

Count each bond once: single=1, double=2, triple=3.

Common element valence electrons

V=1

V=4

V=5

V=6

V=7

V=5

V=6

V=7

Click a tile to set the valence electrons field.

Result

Enter values and press Calculate.

Formula

FC = V − N − B/2

V — valence electrons in the free neutral atom
N — non-bonding (lone pair) electrons on the atom
B — bonding electrons around the atom (bonds × 2)

Worked examples

Atom / molecule	V	N	Bonds	FC
O in H−O−H (water)	6	4	2	0
N in NH⊂4;+ (4 bonds)	5	0	4	+1
O in CO⊂2; (double bond)	6	4	2	0
C in CO⊂2; (two double bonds)	4	0	4	0

Summary

Enter an element symbol (or its valence electrons directly), lone pair electrons, and number of bonds to get the formal charge instantly.

How it works

Select a common element or enter valence electrons manually.
Enter the number of lone pair (non-bonding) electrons on the atom.
Enter the number of bonds around the atom (single=1, double=2, triple=3 each).
The calculator applies FC = V - N - B/2 and displays the result with sign.

Use cases

Determine which Lewis structure resonance form is most stable (lowest formal charges).
Verify atom charges when drawing molecules like CO2, NO2, or SO4²⁻.
Check formal charges on atoms in organic functional groups.
Teach or learn Lewis structure rules with step-by-step charge breakdown.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu