What does this calculator calculate?

It estimates the molecular weight of a polypeptide from its amino acid sequence.

What units are included in the result?

The result includes daltons (Da), kilodaltons (kDa), residue count, and mean mass per residue.

Are spaces and separators allowed in the sequence?

Yes. Spaces and *, - and . separators are ignored, and input is case-insensitive.

How are ambiguity codes handled?

Ambiguity codes such as B, J, O, U, X and Z are not added to the mass calculation but are counted and reported.

Does the result include modifications or disulfide bonds?

No. It represents an unmodified chain and does not account for signal-peptide cleavage, disulfide bonds, post-translational modifications, or tags.

Elysia Tools

Navigation

Education

Protein Molecular Weight Calculator (from Sequence)

MW = Σ ProtParam average residue masses + H₂O, with ambiguity-code handling, kDa/mean-residue output, and unmodified-chain caveats. Educational use only.

Execution

Run this tool

Fill in the form, run the tool, and review the result in one place.

Prepared example runs

Click an example to fill the form automatically. File inputs still need an upload.

2 examples

His-tag MGSSHHHHHHSSGLVPRGSH → 2181.34 Da (20 residues)

The standard 6×His affinity tag from pET vectors (MGSSHHHHHHSSGLVPRGSH — note the seventh His at the C-terminus) sums to 2163.3232 Da of residues plus 18.0152 Da of water = 2181.34 Da, the value usually quoted for this 20-mer. It is the number to subtract when converting an SDS band of a tagged construct back to the tag-free molecular weight.

{"result":"Molecular weight ≈ 2181.34 Da = 2.18 kDa (20 residues, mean 108.17 Da/residue).","metadata":{"input":{"length":20},"result":{"mwDa":2181.34,"mwKda":2.18,"residueCount":20}}}

Every residue once: ACDEFGHIKLMNPQRSTVWY → 2395.74 Da

A self-check sequence containing each of the 20 standard amino acids exactly once (ACDEFGHIKLMNPQRSTVWY) weighs 2395.74 Da including water. It is a quick way to confirm the mass table is intact: the mean residue mass is 118.89 Da, close to the ~110 Da rule of thumb for natural proteins.

{"result":"Molecular weight ≈ 2395.74 Da = 2.4 kDa (20 residues, mean 118.89 Da/residue).","metadata":{"input":{"length":20},"result":{"mwDa":2395.74,"residueCount":20}}}

Inputs

Set the required fields, then run the tool.

2 options

ContentPaste or type the main input values.1

Amino Acid SequencetextareaRequiredOne-letter amino-acid sequence (case-insensitive; spaces and * - . separators are ignored).

SettingsAdjust formats, ranges, numbers, and modes.1

Decimal PlacesnumberOptional

Result

Ready for a run

Run the tool to preview files, text, structured data, or streamed output here.

Samples

Protein Molecular Weight Calculator (from Sequence)

Run this tool

Prepared example runs

Inputs

Result

Examples that match this tool

Continue with connected tools and hubs

Prepared example runs

Inputs

Result

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Estimate the mass of a 6×His affinity tag

2. Check a sequence containing all 20 standard amino acids

FAQ

Web Image Processing Python Samples

Copyright-Free FLAC Audio Samples

Copyright-Free WAV Audio Samples

Android Image Processing Java Samples

Amino Acid Composition Analyzer

Bottleneck Effect Simulator (heterozygosity loss)

Restriction Fragment Length Calculator

Transfection Efficiency Calculator (GFP Positive Rate)

Protein Quantification, Enzyme Kinetics, and Sequence Analysis Tools

Barcode, QR Code, and Label Tools

Audio Encoding and Format Conversion Tools

Image Format Conversion and Animated Export Tools