Why International Journals Require SI Units

in Published Research

Article By Industries Needs

Standardization in scientific literature serves as the bedrock of global research communication, data reproducibility, and collaborative discovery. Over the past century, academic publishers, professional

societies, and peer-reviewed journals across disciplines have systematically transitioned to requiring the International System of Units (Systeme International d'Unites, or SI) for all submitted manuscripts. While legacy non-SI units and regional customary systems persist in daily trade and local contexts, their inclusion in high-impact academic publishing is now strictly restricted or prohibited.

The mandates enforced by editorial boards are not merely bureaucratic preferences. They represent a deliberate, structural effort to safeguard scientific integrity, minimize ambiguity, reduce computational error, and optimize automated data extraction in the digital age.

The Foundations of the International System of Units

Established in 1960 by the 11th General Conference on Weights and Measures (CGPM), the SI framework built upon the older metric system to deliver a coherent, universally applicable measurement baseline. The system is founded upon seven physical base units:

• Length: Meter ($\text{m}$)
  
  
• Mass: Kilogram ($\text{kg}$)
  
  
• Time: Second ($\text{s}$)
  
  
• Electric Current: Ampere ($\text{A}$)
  
  
• Thermodynamic Temperature: Kelvin ($\text{K}$)
  
  
• Amount of Substance: Mole ($\text{mol}$)
  
  
• Luminous Intensity: Candela ($\text{cd}$)
  
  

From these seven base quantities, all other physical measurements—such as force (Newton, $\text{N} = \text{kg}\cdot\text{m/s}^2$), energy (Joule, $\text{J} = \text{N}\cdot\text{m}$), and pressure (Pascal, $\text{Pa} = \text{N/m}^2$)—are derived in a strictly logical, mathematically coherent manner.

Key Drivers Behind Publisher SI Mandates

1. Eliminating Dimensional Ambiguity and Translation Errors

Scientific research is inherently cross-border. When researchers rely on regional, customary, or historical measurement scales, the potential for misinterpretation rises sharply. Non-SI systems often suffer from homonymic confusion—where the same term denotes different magnitudes depending on context or geography:

• Ounces and Gallons: A fluid ounce in the United States Customary System ($\approx 29.57 \text{ mL}$) differs from an Imperial fluid ounce ($\approx 28.41 \text{ mL}$). Similarly, the US gallon ($\approx 3.785 \text{ L}$) differs significantly from the Imperial gallon ($\approx 4.546 \text{ L}$).
  
  
• Tons: The short ton ($2,000 \text{ lbs}$), long ton ($2,240 \text{ lbs}$), and metric tonne ($1,000 \text{ kg} \approx 2,204.62 \text{ lbs}$) introduce substantial variance if left unclarified.
  
  
• Mass vs. Weight: Customary units frequently conflate mass and force (e.g., pound-mass vs. pound-force), introducing implicit conversion factors like standard acceleration due to gravity ($g_0 \approx 9.80665 \text{ m/s}^2$) into basic mechanical equations.
  
  

By enforcing pure SI notation, journals eliminate ambient ambiguity, ensuring that a measured value published in Tokyo carries the exact same mathematical weight when evaluated in Zurich, Nairobi, or Boston.

2. Guarantees of Reproducibility and Interoperability

The cornerstone of the scientific method is independent replication. If an experimental setup cannot be reconstructed precisely from the published methods section, the validity of the work is compromised.

When researchers mix units—such as measuring fluid flow in gallons per minute, pressure in pounds per square inch (psi), and temperatures in Fahrenheit—subsequent investigators must execute multi-step conversions before replicating the experiment. Each conversion step introduces rounding errors, potential transcription mistakes, and cognitive fatigue.

Coherent SI units eliminate unit conversion factors ($\text{factors of } 10^3, 12, 16, 1728$, etc.) from physical equations. In a coherent system, the product or quotient of any two unit quantities yields the derived unit directly:

$$\text{Power (Watts)} = \text{Force (Newtons)} \times \text{Velocity (meters/second)}$$

$$P = F \cdot v$$

No arbitrary numerical scalars are required. This mathematical efficiency streamlines data validation during peer review and minimizes the risk of conversion-induced replication failure.

3. Data Harmonization for Computational Meta-Analysis and AI

Modern scientific discovery increasingly relies on computational synthesis: systematic meta-analyses, cross-study data aggregation, and machine learning models trained on millions of open-access paper texts.

• Automated Data Scraping: Natural Language Processing (NLP) tools and automated extraction algorithms index tables, figures, and text across thousands of journals simultaneously. Unstandardized units force data pipelines to account for dozens of custom conversion dictionaries, increasing the rate of parsing errors.
  
  
• Database Interoperability: Multi-institutional repositories (such as PubChem, GenBank, or EarthChem) rely on standardized schema. Enforcing SI at the point of publication ensures that incoming data streams merge seamlessly into global databases without manual re-curation.
  
  

4. Interdisciplinary Collaboration

Contemporary scientific breakdowns rarely fit neatly inside traditional departmental siloes. Biomedical engineering, climate modeling, nanotechnology, and astrophysics require collaboration across disciplines that historically developed independent unit shorthand.

For instance, a material scientist working on biomechanical implants must communicate with orthopedists, toxicologists, and biomechanists. If the engineer uses Gigapascals ($\text{GPa}$), the clinician uses millimeters of mercury ($\text{mmHg}$), and the mechanics lab uses pounds per square inch ($\text{psi}$), collaborative design breaks down. SI serves as the neutral ground where disparate fields meet.

SI Guidelines Across Major Journal Families

Leading scientific publishers enforce specific requirements regarding unit usage in text, figures, and mathematical expressions:

Publisher / Organization	Scope	SI Mandate Policy	Exceptions / Allowed Non-SI Units
Nature Portfolio	Multidisciplinary	Strictly requires SI or SI-derived units across all titles.	Standard time units ($\text{min}$, $\text{h}$, $\text{d}$), Liter ($\text{L}$), Electronvolt ($\text{eV}$).
Science (AAAS)	General Sciences	Mandates SI units in all main text, tables, and figure axes.	Non-SI units allowed only when reporting original historical data.
ACS (American Chemical Society)	Chemistry & Materials	Requires SI units in accordance with the ACS Style Guide.	Molar concentration ($\text{M} = \text{mol/L}$) widely accepted alongside $\text{mol/m}^3$.
IEEE	Engineering & Tech	Expects metric/SI units in all technical papers and standards.	Legacy units allowed in quotes or parenthetically for hardware specs.
Elsevier / PubMed Central	Medicine & Life Sciences	Mandates SI units; biological metrics require standard SI conversion.	Blood pressure ($\text{mmHg}$) and enzyme activity ($\text{U}$) allowed under medical standards.

Navigating Common Exceptions in Academic Publishing

While SI is the gold standard, editorial boards recognize that certain domain-specific units possess deeply entrenched historical or practical utility. In these cases, journals permit specific non-SI units, provided they are explicitly defined relative to SI standards upon first mention.

1. Units Accepted for Use with SI

Certain non-SI units are so fundamental to human experience or mathematical convenience that the International Committee for Weights and Measures (CIPM) formally accepts them alongside SI:

• Time: Minute ($\text{min} = 60 \text{ s}$), Hour ($\text{h} = 3,600 \text{ s}$), Day ($\text{d} = 86,400 \text{ s}$).
  
  
• Volume: Liter ($\text{L} = 1 \text{ dm}^3 = 10^{-3} \text{ m}^3$).
  
  
• Mass: Tonne ($\text{t} = 10^3 \text{ kg}$).
  
  
• Plane Angle: Degree ($1^\circ = (\pi/180) \text{ rad}$), Minute ($1' = (\pi/10,800) \text{ rad}$), Second ($1'' = (\pi/648,000) \text{ rad}$).
  
  

2. Specialized Domain Conventions

In specialized fields, mandatory conversion to base SI units can obscure practical comprehension:

• Medicine and Physiology: Blood pressure is almost universally reported in millimeters of mercury ($\text{mmHg}$) rather than Pascals ($\text{Pa}$), owing to the standard design of clinical sphygmomanometers. Most medical journals accept $\text{mmHg}$, though some require the equivalent Kilopascal ($\text{kPa}$) value in parentheses.
  
  
• Quantum Physics and Astronomy: Scale extremes make base SI units cumbersome. Particle physicists utilize the electronvolt ($\text{eV}$) for mass-energy, while astronomers use the Astronomical Unit ($\text{au}$), Light-Year ($\text{ly}$), or Parsec ($\text{pc}$) to quantify galactic distances.
  
  
• Crystallography and Atomic Scale: The Ångström ($\text{Å} = 10^{-10} \text{ m} = 0.1 \text{ nm}$) remains widely used in structural biology and crystallography to describe atomic bonds, though many modern journals encourage nanometers ($\text{nm}$) or picometers ($\text{pm}$).
  
  

Best Practices for Authors Preparing Manuscripts

To avoid formatting revisions or desk rejections during initial editorial screening, researchers should adhere to the following workflow when preparing measurement data:

1. Audit Raw Data Early: Convert instruments' proprietary outputs (such as empirical voltage readings, customary scale measurements, or raw sensor values) into SI units during the initial data processing phase, rather than during final manuscript drafting.
   
   
2. Consult Journal-Specific Author Guidelines: Review the target journal's specific instructions for authors regarding preferred abbreviations, permitted non-SI units, and formatting conventions for compound units (e.g., using negative exponents $\text{m}\cdot\text{s}^{-1}$ vs. slashes $\text{m/s}$).
   
   
3. Format Compound Units Consistently: Avoid mixing slashes in complex expressions. Write $\text{J}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$ or $\text{J}/(\text{kg}\cdot\text{K})$ rather than $\text{J}/\text{kg}/\text{K}$.
   
   
4. Maintain Proper Symbol Syntax:
   
   
   • Leave a space between the numerical value and the unit symbol (e.g., $25 \text{ kg}$, not $25kg$), except for degree symbols used for plane angles ($45^\circ$).
     
     
   • Keep unit symbols lowercased unless derived from a proper name (e.g., $h$ for hours vs. $N$ for Isaac Newton, $Hz$ for Heinrich Hertz, $Pa$ for Blaise Pascal).
     
     
   • Do not pluralize unit symbols (e.g., $10 \text{ kg}$, never $10 \text{ kgs}$).
     
     
5. Annotate Legacy References Clear-Cut: When referencing historical studies that utilized legacy units (e.g., calories, bar, feet), state the original measurement followed immediately by the modern SI equivalent in parentheses: "The reaction was maintained at 30 psi (206.8 kPa)..."
   
   

The Future of Universal Measurement in Publishing

As scientific research moves toward open data standards, automated synthesis, and cloud-based laboratory execution, the enforcement of SI units in published research is becoming increasingly stringent. Standardizing measurement language across scientific journals ensures that current discoveries remain clear, actionable, and reproducible for future generations of global researchers.

Accuracy vs. Precision in Science:

SI Units and Laboratory Accreditation:

Common SI Unit Conversion Errors