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Chemistry

Molecular Weight Calculator

Compute molecular weight. Free online Molecular Weight Calculator. Calculate molecular weight online — fast, accurate, mobile-friendly, no signup needed.

Enter atom counts (H, C, O, N). Uses standard atomic weights.

Molecular weight (g/mol)
14.027

Derivation

  1. ├── 01GivenH = 2, C = 1, O = 0, N = 0
  2. ├── 02Formula1.008 × e.H+12.011 × e.C+15.999 × e.O+14.007 × e.N
  3. ├── 03Substitute1.008 × e.2+12.011 × e.1+15.999 × e.0+14.007 × e.0
  4. └── 04Compute Molecular weight (g/mol)14.027
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§01What is

Understanding the Molecular Weight Calculator

The Molecular Weight Calculator computes Molecular weight (g/mol) from 4 inputs: h atoms, c atoms, o atoms, n atoms. Compute molecular weight.

Chemistry turns grams and moles into reactions. Getting the stoichiometry, dilutions, or concentrations right is the difference between a lab result you can trust and one you can’t reproduce. The Molecular Weight Calculator sits in that toolkit — it compute molecular weight. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

1.008 × e.H+12.011 × e.C+15.999 × e.O+14.007 × e.N

Where

H
H atoms
C
C atoms
O
O atoms
N
N atoms
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: H atoms = 2, C atoms = 1, O atoms = 0, N atoms = 0.

  1. 01Start by noting the input — H atoms: 2.
  2. 02Start by noting the input — C atoms: 1.
  3. 03Start by noting the input — O atoms: 0.
  4. 04Start by noting the input — N atoms: 0.
  5. 05Substitute these values into the formula: 1.008 × e.H+12.011 × e.C+15.999 × e.O+14.007 × e.N
  6. 06Compute Molecular weight (g/mol): the calculator returns 14.027.
  7. 07Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Molecular Weight Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

H atoms halved

H = 1 (from 2)

Keep every other input at its default and halve the h atoms. See how molecular weight (g/mol) responds.

  1. 01New H atoms: 1
  2. 02Baseline Molecular weight (g/mol): 14.027
  3. 03New Molecular weight (g/mol): 13.019
  4. 04Molecular weight (g/mol) decreases by 7.2% → use this sensitivity to plan for real-world variation.
02 · PATTERN

H atoms doubled

H = 4 (from 2)

Keep every other input at its default and double the h atoms. See how molecular weight (g/mol) responds.

  1. 01New H atoms: 4
  2. 02Baseline Molecular weight (g/mol): 14.027
  3. 03New Molecular weight (g/mol): 16.043
  4. 04Molecular weight (g/mol) increases by 14.4% → use this sensitivity to plan for real-world variation.
03 · PATTERN

C atoms halved

C = 0.5 (from 1)

Keep every other input at its default and halve the c atoms. See how molecular weight (g/mol) responds.

  1. 01New C atoms: 0.5
  2. 02Baseline Molecular weight (g/mol): 14.027
  3. 03New Molecular weight (g/mol): 8.0215
  4. 04Molecular weight (g/mol) decreases by 42.8% → use this sensitivity to plan for real-world variation.
04 · PATTERN

C atoms doubled

C = 2 (from 1)

Keep every other input at its default and double the c atoms. See how molecular weight (g/mol) responds.

  1. 01New C atoms: 2
  2. 02Baseline Molecular weight (g/mol): 14.027
  3. 03New Molecular weight (g/mol): 26.038
  4. 04Molecular weight (g/mol) increases by 85.6% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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