A Template for Lab Notebooks

Article By Industries Needs

Accurate physical measurement is the undisputed bedrock of reproducible science. Whether you are preparing buffer solutions for cell culture, calibrating high-performance liquid chromatography (HPLC) columns, or calculating enzyme kinetics, moving between units of measure is an everyday necessity. Yet, despite years of training, simple mathematical slips during unit conversions remain one of the leading causes of experimental failure, wasted reagents, and irreproducible research.

Creating a dedicated SI Conversion Cheat Sheet tailored to your specific field and pasting it inside the front cover of your physical lab notebook—or keeping it pinned in your electronic lab notebook (ELN)—provides a quick, low-tech, and foolproof safeguard. This comprehensive guide outlines the fundamental principles of the International System of Units (SI), details the key conversion factors across major scientific disciplines, and provides a customizable template designed specifically for daily laboratory use.

1. The Core Architecture of the SI System

The International System of Units (SI) is built upon seven fundamental base units from which all other scientific quantities are derived. Understanding how these base units interact prevents dimensional errors when working with complex metric prefixes or non-SI units.

The 7 Core SI Base Units

Dimension / Quantity	Base Unit Name	Symbol	Fundamental Physical Constant / Definition Basis
Length	meter	$\text{m}$	Speed of light in vacuum ( $c = 299,792,458 \text{ m/s}$ )
Mass	kilogram	$\text{kg}$	Planck constant ( $h = 6.62607015 \times 10^{-34} \text{ J}\cdot\text{s}$ )
Time	second	$\text{s}$	Hyperfine transition frequency of Caesium-133 ( $\Delta \nu_{\text{Cs}}$ )
Electric Current	ampere	$\text{A}$	Elementary charge ( $e = 1.602176634 \times 10^{-19} \text{ C}$ )
Thermodynamic Temp.	kelvin	$\text{K}$	Boltzmann constant ( $k = 1.380649 \times 10^{-23} \text{ J/K}$ )
Amount of Substance	mole	$\text{mol}$	Avogadro constant ( $N_{\text{A}} = 6.02214076 \times 10^{23} \text{ mol}^{-1}$ )
Luminous Intensity	candela	$\text{cd}$	Luminous efficacy of $540 \text{ THz}$ monochromatic radiation

Derived SI Units Commonly Encountered in Bench Work

Force: Newton ( $\text{N}$ ) $\rightarrow \text{kg}\cdot\text{m}\cdot\text{s}^{-2}$
Pressure: Pascal ( $\text{Pa}$ ) $\rightarrow \text{N/m}^2 = \text{kg}\cdot\text{m}^{-1}\cdot\text{s}^{-2}$
Energy / Work: Joule ( $\text{J}$ ) $\rightarrow \text{N}\cdot\text{m} = \text{kg}\cdot\text{m}^2\cdot\text{s}^{-2}$
Power: Watt ( $\text{W}$ ) $\rightarrow \text{J/s} = \text{kg}\cdot\text{m}^2\cdot\text{s}^{-3}$
Electric Charge: Coulomb ( $\text{C}$ ) $\rightarrow \text{A}\cdot\text{s}$
Frequency: Hertz ( $\text{Hz}$ ) $\rightarrow \text{s}^{-1}$

2. Navigating Orders of Magnitude: SI Prefixes

Modern bench techniques operate across extreme scale variations—ranging from femtoliter microfluidic droplets to gigapascal pressure chambers. Memorizing key powers of ten speeds up quick estimations and sanity checks during experimental runs.

Prefix	Symbol	Factor (Decimal)	Scientific Notation	Common Bench Example
Giga-	$\text{G}$	$1,000,000,000$	$10^{9}$	Gigahertz ( $\text{GHz}$ ) CPU clock speeds
Mega-	$\text{M}$	$1,000,000$	$10^{6}$	Megapascal ( $\text{MPa}$ ) high-pressure chromatography
Kilo-	$\text{k}$	$1,000$	$10^{3}$	Kilogram ( $\text{kg}$ ), Kilobase ( $\text{kb}$ ) DNA lengths
(Base Unit)	—	$1$	$10^{0}$	Meter ( $\text{m}$ ), Gram ( $\text{g}$ ), Liter ( $\text{L}$ )
Milli-	$\text{m}$	$0.001$	$10^{-3}$	Milligram ( $\text{mg}$ ), Milliliter ( $\text{mL}$ )
Micro-	$\mu$	$0.000001$	$10^{-6}$	Microliter ( $\mu\text{L}$ ), Micrometer ( $\mu\text{m}$ )
Nano-	$\text{n}$	$0.000000001$	$10^{-9}$	Nanogram ( $\text{ng}$ ), Nanometer ( $\text{nm}$ ) wavelength
Pico-	$\text{p}$	$0.000000000001$	$10^{-12}$	Picomolar ( $\text{pM}$ ) primer concentrations
Femto-	$\text{f}$	$0.000000000000001$	$10^{-15}$	Femtoliter ( $\text{fL}$ ) single-cell volumes

3. High-Frequency Lab Conversions by Discipline

Depending on whether you work in biochemistry, analytical chemistry, or physics, your daily conversion needs will vary. Below are quick-reference tables tailored to primary laboratory domains.

A. Solution Preparation & Molecular Biology

Concentration calculations represent one of the highest sources of dilution error. The non-SI unit "Molar" (

\text{M}

) remains standard in chemistry, defined explicitly as moles per liter (

\text{mol/L}

Volume Equivalence:
- $1 \text{ L} = 1 \text{ dm}^3 = 1,000 \text{ mL} = 10^{-3} \text{ m}^3$
- $1 \text{ mL} = 1 \text{ cm}^3 = 1 \text{ cc} = 1,000 \text{ }\mu\text{L}$
- $1 \text{ }\mu\text{L} = 1,000 \text{ nL}$
Mass & Mass Equivalence:
- $1 \text{ kg} = 1,000 \text{ g} = 10^6 \text{ mg}$
- $1 \text{ g} = 1,000 \text{ mg} = 10^6 \text{ }\mu\text{g} = 10^9 \text{ ng}$
- $1 \text{ Dalton (Da)} = 1 \text{ amu} \approx 1.66054 \times 10^{-27} \text{ kg} \approx 1 \text{ g/mol}$
Molarity Scaling:
- $1 \text{ M} = 1 \text{ mol/L} = 1 \text{ mmol/mL} = 1 \text{ }\mu\text{mol/}\mu\text{L}$
- $1 \text{ mM} = 10^{-3} \text{ M} = 1 \text{ }\mu\text{mol/mL} = 1 \text{ nmol/}\mu\text{L}$
- $1 \text{ }\mu\text{M} = 10^{-6} \text{ M} = 1 \text{ nmol/mL} = 1 \text{ pmol/}\mu\text{L}$
- $1 \text{ nM} = 10^{-9} \text{ M} = 1 \text{ pmol/mL} = 1 \text{ fmol/}\mu\text{L}$
Percent Solution Shortcuts:
- $1\% \text{ w/v} = 1 \text{ g per } 100 \text{ mL} = 10 \text{ mg/mL} = 10,000 \text{ }\mu\text{g/mL}$
- $1\% \text{ v/v} = 1 \text{ mL solute per } 100 \text{ mL solution}$
- $1 \text{ ppm (parts per million)} = 1 \text{ mg/L} = 1 \text{ }\mu\text{g/mL}$ (in dilute aqueous media)
- $1 \text{ ppb (parts per billion)} = 1 \text{ }\mu\text{g/L} = 1 \text{ ng/mL}$

B. Pressure & Vacuum Systems

Vacuum manifolds, gas cylinders, and pressure vessels regularly mix imperial, CGS, and SI metric units.

To Convert From	To SI Unit	Multiply By
Atmosphere ( $\text{atm}$ )	Pascal ( $\text{Pa}$ )	$101,325$
Atmosphere ( $\text{atm}$ )	Kilopascal ( $\text{kPa}$ )	$101.325$
Bar ( $\text{bar}$ )	Pascal ( $\text{Pa}$ )	$100,000$ ( $10^5$ )
Millimeter of Mercury ( $\text{mmHg}$ ) / Torr	Pascal ( $\text{Pa}$ )	$133.322$
Pounds per Square Inch ( $\text{psi}$ )	Kilopascal ( $\text{kPa}$ )	$6.89476$

Quick Pressure Reference: $1 \text{ atm} = 101.325 \text{ kPa} = 1.01325 \text{ bar} = 760 \text{ Torr} = 14.696 \text{ psi}$

C. Temperature Conversions & Energy Equivalents

While Celsius (

\text{°C}

) is standard practice on bench thermometers, thermodynamic calculations (e.g., Gibbs free energy, Arrhenius rate constants) require Kelvin (

\text{K}

Celsius to Kelvin: $T_{\text{K}} = T_{\text{°C}} + 273.15$
Fahrenheit to Celsius: $T_{\text{°C}} = (T_{\text{°F}} - 32) \times \frac{5}{9}$
Energy Units:
- $1 \text{ calorie (cal)} = 4.184 \text{ Joules (J)}$
- $1 \text{ kcal/mol} = 4.184 \text{ kJ/mol}$
- $1 \text{ electronvolt (eV)} = 1.60218 \times 10^{-19} \text{ J}$

4. The Factor-Label Method (Dimensional Analysis)

The single most effective tool against unit conversion errors is the factor-label method (or dimensional analysis). This approach treats unit labels as algebraic terms that cancel out step-by-step.

Step-by-Step Execution Strategy

Identify Given and Desired Units: State your starting quantity clearly with its full unit expression.
Set Up Unit Equivalences as Fractions: Write conversion factors so that the unit you want to eliminate is in the opposite position (numerator vs. denominator).
Multiply Across: Perform the scalar multiplication/division only after confirming that every unwanted unit cancels out cleanly.

Worked Example: Protein Quantitation Adjustment

Scenario: You measure a protein sample concentration of

3.5 \text{ }\mu\text{g/}\mu\text{L}

. You need to calculate how many grams of protein are contained in a

2.5 \text{ L}

solution batch.

\text{Target Mass (g)} = 2.5 \text{ L} \times \left( \frac{1,000 \text{ mL}}{1 \text{ L}} \right) \times \left( \frac{1,000 \text{ }\mu\text{L}}{1 \text{ mL}} \right) \times \left( \frac{3.5 \text{ }\mu\text{g}}{1 \text{ }\mu\text{L}} \right) \times \left( \frac{1 \text{ g}}{10^6 \text{ }\mu\text{g}} \right)

Step 1 (Cancel Liters): $2.5 \text{ L} \times \frac{1,000 \text{ mL}}{1 \text{ L}} = 2,500 \text{ mL}$
Step 2 (Cancel Milliliters): $2,500 \text{ mL} \times \frac{1,000 \text{ }\mu\text{L}}{1 \text{ mL}} = 2.5 \times 10^6 \text{ }\mu\text{L}$
Step 3 (Calculate Micrograms): $2.5 \times 10^6 \text{ }\mu\text{L} \times \frac{3.5 \text{ }\mu\text{g}}{1 \text{ }\mu\text{L}} = 8.75 \times 10^6 \text{ }\mu\text{g}$
Step 4 (Cancel Micrograms to Grams): $8.75 \times 10^6 \text{ }\mu\text{g} \times \frac{1 \text{ g}}{10^6 \text{ }\mu\text{g}} = 8.75 \text{ g}$
Result: $8.75 \text{ g}$ of protein.

5. Lab Notebook Template: Print-Ready Reference Block

Cut out or transcribe the following structured cheat sheet template into the opening pages of your lab notebook.

Plaintext

================================================================================
                    LABORATORY SI CONVERSION CHEAT SHEET
================================================================================

[1] CORE CONCENTRATIONS & VOLUMES
    • 1 M   = 1 mol/L  = 1 mmol/mL = 1 µmol/µL
    • 1 mM  = 10⁻³ M   = 1 µmol/mL = 1 nmol/µL
    • 1 µM  = 10⁻⁶ M   = 1 nmol/mL = 1 pmol/µL
    • 1 nM  = 10⁻⁹ M   = 1 pmol/mL = 1 fmol/µL
    ----------------------------------------------------------------------------
    • 1 L = 1,000 mL = 10⁶ µL | 1 mL = 1 cm³ = 1,000 µL | 1 µL = 1,000 nL
    • 1 g = 1,000 mg = 10⁶ µg = 10⁹ ng | 1 Da ≈ 1 g/mol

[2] DILUTION FORMULAS & PERCENT SOLUTIONS
    • Stock Dilution: C₁V₁ = C₂V₂  (Units for C and V MUST be identical)
    • Mass/Vol %:    1% w/v = 1 g / 100 mL = 10 mg/mL = 10 µg/µL
    • PPM / PPB:     1 ppm = 1 mg/L = 1 µg/mL  |  1 ppb = 1 µg/L = 1 ng/mL

[3] PRESSURE & VACUUM EQUIVALENCES
    • 1 atm = 101.325 kPa = 1.01325 bar = 760 Torr = 760 mmHg = 14.696 psi
    • 1 bar = 100 kPa = 10⁵ Pa

[4] TEMPERATURE & ENERGY
    • K = °C + 273.15      | °C = (°F - 32) × (5/9)
    • 1 cal = 4.184 J      | 1 kcal/mol = 4.184 kJ/mol

[5] COMMON PHYSICAL CONSTANTS (3 Significant Figures)
    • Avogadro's Number (N_A) : 6.02 × 10²³ mol⁻¹
    • Universal Gas Constant (R): 8.314 J/(mol·K) = 0.0821 (L·atm)/(mol·K)
    • Faraday Constant (F)     : 96,485 C/mol
    • Speed of Light (c)       : 3.00 × 10⁸ m/s
    • Planck's Constant (h)    : 6.63 × 10⁻³⁴ J·s

================================================================================

6. Best Practices for Documenting Units in Experimental Records

Beyond keeping a quick-reference chart, consistent documentation habits prevent ambiguity when reviewing entry logs weeks or years later.

Never Record "Bare" Numbers: Always write $12.5 \text{ mL}$ or $0.45 \text{ g}$ , never just $12.5$ or $0.45$ . Unlabeled numerical entries create severe compliance and auditing issues.
Standardize Unit Abbreviations: Stick strictly to official IUPAC/SI symbols. Use $\text{s}$ for seconds (not $\text{sec}$ ), $\text{h}$ for hours (not $\text{hrs}$ ), and $\text{L}$ or $\text{l}$ for liters (avoid vague abbreviations like $\text{ltr}$ ).
Maintain Significant Figures Across Conversions: Your final converted value should never imply a higher degree of precision than your original measuring instrument. For example, if an analytical balance weighs to three decimal places ( $0.125 \text{ g}$ ), converting that value to milligrams should be recorded as $125 \text{ mg}$ , not $125.000 \text{ mg}$ .
Label Centrifugation in Relative Centrifugal Force ( $\text{RCF} \times g$ ): Avoid recording centrifugation protocols solely in revolutions per minute ( $\text{RPM}$ ). $\text{RPM}$ varies based on the rotor radius ( $r$ ), whereas $g$ -force ( $\text{RCF}$ ) is universal across different centrifuge models:

\text{RCF} = 1.118 \times 10^{-5} \times r \times (\text{RPM})^2

(where $r$ is the rotor radius in centimeters).

By taking thirty minutes to transcribe and customize this cheat sheet template into your primary lab notebook, you establish a reliable operational standard that safeguards your calculations, speeds up daily preparation, and ensures experimental rigor.

Digital Tools vs. Manual Calculation:

Sunday, August 9, 2026

Building Your Own SI Conversion Cheat Sheet: