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MDCAT Important Constants, Units & Reference Values

A compact reference of fundamental constants, common conversion anchors and carefully labeled approximate biological values. Exact defined constants are separated from context-dependent reference values.

Study Tools / Informational / MDCAT Important Constants, Units & Reference Values
Research edition · Updated 19 September 2026 · Built for MDCAT study and reference
Research note: This page combines PM&DC curriculum context with standard scientific references. It is designed as a study aid; the current official syllabus and examination notices remain the source of truth for exam-specific requirements.
c
299,792,458 m/s — exact
N_A
6.02214076×10²³ mol⁻¹ — exact
R
8.314462618 J mol⁻¹ K⁻¹
Official-context note: Not every value on this page should be treated as an exam-given constant. Some are exact SI-defined values, some are widely used physical constants, and some biological quantities vary with textbook, population and clinical context. Always follow values supplied in the question or the conventions expected by the syllabus.

Quick Reference

Quick take

Exact is not approximate

The speed of light and elementary charge have exact SI definitions; g near Earth is a practical approximation.

Quick take

Use K for gas laws

Absolute temperature is required in relationships such as PV = nRT.

Quick take

Carry units

A constant without its unit is easy to misuse.

Quick take

Biology values vary

Normal ranges and physiological measurements can depend on the reference source.

1. Exact / Defined Constants

ConstantSymbolValueUnit
Speed of light in vacuumc299,792,458m/s
Elementary chargee1.602176634 × 10⁻¹⁹C
Planck constanth6.62607015 × 10⁻³⁴J·s
Avogadro constantNA6.02214076 × 10²³mol⁻¹
Boltzmann constantk1.380649 × 10⁻²³J/K

2. Common Physical Constants

QuantityTypical valueUnitNote
Gravitational constant6.67430 × 10⁻¹¹N·m²/kg²Use supplied values when given.
Universal gas constant8.314462618J·mol⁻¹·K⁻¹May be rounded in classroom problems.
Standard gravity9.80665m/s²Defined standard value; local g is approximate.
Standard atmosphere101,325PaReference pressure.
Faraday constant≈ 96485C/molDerived from eNA; often rounded.

3. Chemistry Anchors

Temperature

K = °C + 273.15

Use the absolute scale in gas-law and thermodynamic relationships that require kelvin.

Volume

1 L = 10⁻³ m³

Useful when moving between molarity contexts and SI volume.

Pressure

1 atm = 101325 Pa

Check whether a problem uses atm, kPa, mmHg or Pa.

Amount

1 mol = 6.022…×10²³ entities

The amount-of-substance scale connecting microscopic particles and macroscopic samples.

4. Biology Reference Values Need Context

Unlike SI-defined constants, many biological measurements are not universal constants. Human body temperature, blood pressure, cell counts and biochemical ranges vary with measurement method, population, environment and reference source. For MDCAT, use the value stated in your textbook or question when a numerical value is required.

Good exam habit: if a question gives a value, use that value. Do not substitute a memorized “normal” just because it looks familiar.

5. Prefix & Power-of-Ten Anchors

PowerPrefixSymbol
10⁶megaM
10³kilok
10⁻²centic
10⁻³millim
10⁻⁶microμ
10⁻⁹nanon
10⁻¹²picop

Frequently Asked Questions

Should I memorize all constants?
Memorize the core values your syllabus and textbook expect, but focus especially on unit awareness and scientific notation. Many exams supply selected constants in the question.
Is g exactly 9.8 m/s²?
9.8 or 9.81 m/s² is a common approximation near Earth. Standard gravity has a defined value of 9.80665 m/s², while local gravitational acceleration varies.
Are biological “normal values” fixed?
No. Many depend on reference intervals and measurement conditions. For exam questions, use the value or range specified by the course source.
Why separate exact constants from approximate values?
Because replacing an exact definition with a rough school value is fine for some calculations but not for others. Knowing the distinction prevents false precision.
Research & reference sources:
PM&DC — Uniform Curriculum MDCAT-2025 (official PDF) · NIST — Metric (SI) Prefixes · NIST — Guide to the SI, Chapter 4 · OpenStax — College Physics 2e: Physical Quantities, Units, Accuracy & Significant Figures

Scope: scientific explanations are written for student use and simplified where appropriate. Exact exam wording, syllabus scope and current administrative rules should be checked against PM&DC documents.