liminfoMolecular Weight Calculator
Free reference guide: Molecular Weight Calculator
About Molecular Weight Calculator
The Molecular Weight Reference is a comprehensive, searchable lookup tool for scientists and students working in chemistry, biochemistry, and life sciences laboratories. It provides instant access to atomic weights of key elements (H, C, N, O, S, P, Na), molecular weights of common compounds (water, NaCl, glucose, ethanol), and detailed buffer preparation recipes for Tris-HCl, EDTA, SDS, and PBS.
Beyond simple MW lookup, this reference includes practical concentration calculation formulas: molarity (M = n/V), mass percent (w/v%, w/w%), the C1V1 = C2V2 dilution equation, and ppm/ppb conversions. Each entry shows the complete formula with worked examples so you can prepare solutions confidently without pulling out a textbook.
The biochemical reagent section covers ATP, dNTPs, amino acid residue averages, DNA/RNA molecular weight estimation rules (660 Da/bp for dsDNA, 330 Da/nt for ssDNA), BSA protein standard data, and even the Du Bois body surface area formula. All data is organized into five searchable categories and runs entirely in your browser with no server calls.
Key Features
- Atomic weights for H, C, N, O, S, P, Na with isotope distributions and electron configurations
- Molecular weights for water, NaCl, glucose, ethanol with density and molar concentration data
- Step-by-step buffer preparation recipes for Tris-HCl, EDTA (pH 8.0), SDS, and 10x/1x PBS
- Molarity, mass percent, C1V1=C2V2 dilution, and ppm/ppb concentration calculation formulas with worked examples
- Biochemical reagent data for ATP, dNTPs, amino acids, DNA/RNA MW estimation, and BSA standards
- Category-based filtering across Atomic Weights, Common Molecules, Buffers/Reagents, Concentration, and Biochemical Reagents
- Instant keyword search to find any element, compound, or formula in seconds
- Bilingual Korean/English interface with full dark mode support on all devices
Frequently Asked Questions
What molecular weight data does this reference include?
It covers atomic weights for seven key elements (H, C, N, O, S, P, Na) with isotope information, molecular weights for common laboratory compounds (H2O, NaCl, glucose, ethanol), buffer reagent MWs (Tris base, Tris-HCl, EDTA, EDTA-2Na, SDS), and biochemical reagent MWs (ATP, dNTPs, BSA, DNA/RNA per-base averages).
How do I use the buffer preparation recipes?
Each buffer entry shows the exact mass of reagent needed, the target volume, pH adjustment instructions, and any special notes. For example, the 0.5 M EDTA (pH 8.0) recipe specifies 186.12 g of EDTA-2Na per liter and notes that approximately 20 g NaOH is needed for dissolution and pH adjustment.
Can I calculate molarity and dilutions with this tool?
Yes. The Concentration section includes the molarity formula M = (m / MW) / V with worked examples, mass percent formulas (w/v% and w/w%), and the C1V1 = C2V2 dilution equation with practical examples like diluting 10x PBS to 1x or making 1 M HCl from 12 M stock.
How do I estimate the molecular weight of a protein or DNA fragment?
For proteins, multiply the number of amino acid residues by 110 Da (average residue MW after water removal). For dsDNA, use 660 Da per base pair; for ssDNA, 330 Da per nucleotide; for ssRNA, 340 Da per nucleotide. A 1 kb dsDNA fragment is approximately 660 kDa.
What is the difference between ppm and ppb?
1 ppm equals 1 mg/L (or 1 ug/mL), while 1 ppb equals 1 ug/L (or 1 ng/mL). The reference includes conversion examples and real-world context, such as the EPA lead limit in drinking water of 15 ppb (0.015 mg/L).
Does this reference cover A260 absorbance conversions for nucleic acids?
Yes. The DNA/RNA MW entry includes A260 absorbance conversion factors: 1 A260 unit corresponds to 50 ug/mL for dsDNA, 33 ug/mL for ssDNA, and 40 ug/mL for RNA. These are essential for spectrophotometric quantification.
Is the BSA entry about the protein or body surface area?
Both are included. Bovine Serum Albumin (the protein standard) has MW 66,463 Da, 583 amino acids, pI 4.7, and extinction coefficient 43,824 M-1cm-1. The body surface area (BSA) entry provides the Du Bois formula: BSA(m2) = 0.007184 * W^0.425 * H^0.725.
Is this reference free to use?
Yes, completely free with no sign-up, no download, and no usage limits. All data is loaded client-side in your browser, so nothing is sent to any server. It works on desktop, tablet, and mobile devices with full dark mode support.