Physics Constants List: Values, Units, and When to Use Them

Overview

Here is the quick-reference version first. The values below are the ones many students see most often in introductory physics, high school physics, AP courses, and first-year college classes. Teachers and exam boards may round slightly differently, so always use the value provided on your formula sheet or in the problem if one is given.

Common physics constants list

• Speed of light in vacuum, c = 3.00 × 10⁸ m/s
• Gravitational acceleration near Earth, g = 9.8 m/s² (sometimes 9.81 m/s², or 10 m/s² for estimation)
• Universal gravitational constant, G = 6.67 × 10⁻¹¹ N·m²/kg²
• Coulomb constant, k = 8.99 × 10⁹ N·m²/C²
• Elementary charge, e = 1.60 × 10⁻¹⁹ C
• Mass of electron, m_e = 9.11 × 10⁻³¹ kg
• Mass of proton, m_p = 1.67 × 10⁻²⁷ kg
• Planck constant, h = 6.63 × 10⁻³⁴ J·s
• Reduced Planck constant, ħ = 1.05 × 10⁻³⁴ J·s
• Vacuum permittivity, ε₀ = 8.85 × 10⁻¹² C²/(N·m²)
• Vacuum permeability, μ₀ = 4π × 10⁻⁷ T·m/A
• Avogadro constant, N_A = 6.02 × 10²³ mol⁻¹
• Universal gas constant, R = 8.31 J/(mol·K)
• Boltzmann constant, k_B = 1.38 × 10⁻²³ J/K
• Stefan–Boltzmann constant, σ = 5.67 × 10⁻⁸ W/(m²·K⁴)

Not every student needs every constant on every test. In mechanics, you will use g far more often than h. In electrostatics, k and e matter more than G. In modern physics, c and h appear repeatedly. The purpose of a reference page is not to memorize everything blindly. It is to connect each constant to a family of problems.

If you often lose points because of unit errors, it also helps to pair this page with Dimensional Analysis in Physics: How to Check Equations and Catch Mistakes. Constants are only useful when their units fit the equation you are using.

Core concepts

The most useful way to learn common constants in physics is to group them by topic and ask one question: what kind of problem tells me this constant belongs here? That is more reliable than trying to memorize a long table without context.

1. Mechanics and gravity constants

g: gravitational acceleration near Earth

Use g when a problem involves falling objects, projectile motion, inclined planes, pendulums at an introductory level, or weight near Earth’s surface. In many physics homework help situations, students mix up g and G. They are not interchangeable.

• g is the local acceleration due to gravity near Earth.
• Units: m/s²
• Typical use: weight, free fall, vertical motion, projectile motion

Examples:

• Weight: F = mg
• Vertical displacement: y = v₀t − (1/2)gt²

G: universal gravitational constant

Use G in Newton’s law of universal gravitation, usually when two masses attract each other across a distance. This appears in planetary motion, satellites, astronomy-style problems, and some AP Physics C mechanics study guide topics.

• G = 6.67 × 10⁻¹¹ N·m²/kg²
• Typical use: F = Gm₁m₂/r²

A quick memory tip: lowercase g is local and practical; uppercase G is universal and astronomical.

2. Electromagnetism constants

k: Coulomb constant

Use k in electric force and electric field problems involving point charges.

• Electric force: F = kq₁q₂/r²
• Electric field: E = kq/r²

If you are doing electric circuits practice, you may not need k very often. But in electrostatics and field questions, it appears constantly.

e: elementary charge

Use e when a problem refers to the charge of a proton, electron, or an integer multiple of basic charge. This is common in atomic and particle problems.

• Charge of one proton: +e
• Charge of one electron: −e

ε₀ and μ₀

These appear more often in college introductory physics study support and electromagnetism than in basic high school courses, but students do see them in electric field, capacitance, electromagnetic waves, and magnetism formulas. They also help explain why the speed of light can be written in terms of electric and magnetic constants.

3. Modern physics constants

c: speed of light value

This is one of the most recognized constants in physics. Students first meet it in wave equations and later in relativity and quantum topics.

• Wave relation: c = fλ for electromagnetic waves in vacuum
• Relativity: E = mc²

Do not automatically use c for sound or water waves. For those, you use the wave speed given by the medium, not the speed of light.

h: Planck constant

Use h in photon energy and quantum relations:

• E = hf
• λ = h/p

This becomes especially useful if you are reviewing modern physics basics alongside Modern Physics Basics: Photoelectric Effect, Atomic Models, and Nuclear Decay.

ħ: reduced Planck constant

This appears more in higher-level quantum formulas. Many high school students can recognize it without needing it often, but college students should know it as h divided by 2π.

4. Particle masses

m_e and m_p are useful in atomic models, charge-to-mass ratio ideas, and momentum or energy calculations involving particles. In many introductory courses, you are more likely to be given these values when needed rather than expected to memorize them.

5. Thermal physics and gas constants

R: universal gas constant

Use R in the ideal gas law when the amount of substance is in moles:

• PV = nRT

k_B: Boltzmann constant

Use k_B when working at the particle level rather than the mole level. A common form is:

• PV = Nk_BT

N_A: Avogadro constant

This connects particles and moles. If you are converting between microscopic and macroscopic descriptions, N_A is often the bridge.

σ: Stefan–Boltzmann constant

This appears in thermal radiation problems and is more common in broader introductory physics than in a first mechanics-only course.

Related terms

This section clears up the language around constants, units, and formulas so you can use your physics constants list correctly.

Constant vs variable

A constant has a fixed value in the context of physics laws, while a variable can change from problem to problem. For example, in projectile motion, g is often treated as constant near Earth, but the initial velocity and launch angle are variables.

Constant vs conversion factor

These are not the same thing. A constant like c or G belongs to a physical law. A conversion factor like 100 cm = 1 m is used to change units. Students sometimes blend the two when rushing through physics exam practice.

Value vs rounded value

Many constants are written in shortened form for classroom use. That is normal. On tests, precision usually depends on the significant figures required by the data in the problem. If a formula sheet gives 9.8 m/s², use that instead of switching to 9.81 unless your instructor says otherwise.

SI units

Most standard constants are given in SI units. That matters because formulas are usually built to work directly with meters, kilograms, seconds, coulombs, kelvin, and moles. If you plug centimeters into an equation without converting them to meters, the constant will not rescue the calculation.

Derived units

Some constants use derived units like newtons, joules, tesla, or volts. If these feel abstract, break them apart into base units when checking your work. This is a useful habit for physics problem solver steps and a major source of fewer mistakes over time.

Formula sheet culture

Different courses expect different levels of memorization. Some AP Physics prep settings provide a formula sheet. Some classroom tests expect you to know a small set of constants from memory. This is why your study method should include two layers: recognize the constant and know the equation family it belongs to.

Practical use cases

This is where a constants page becomes a real study tool. The goal is not just to look up numbers. The goal is to know when to reach for them quickly and confidently.

Use case 1: Choosing the right constant from a word problem

Ask these questions:

1. What topic is this problem really about: motion, gravity, electricity, waves, thermal physics, or modern physics?
2. Is the setting near Earth’s surface, or is it about masses attracting across space?
3. Am I working with point charges, particles, photons, or gases?
4. What units are already present in the givens?

Example: “A ball is thrown upward from the ground.” That points to g, not G. Example: “Two spheres of mass attract each other in space.” That points to G, not g.

Use case 2: Building a shorter exam-day constants sheet

For physics test prep, make a personalized one-page list with three columns:

• Constant
• Value and units
• Use it when...

That third column matters most. Instead of writing only “k = 8.99 × 10⁹,” write “use for electric force and electric field of point charges.” This turns memorization into retrieval by context.

Use case 3: Catching unit mistakes before they cost points

Before substituting numbers, check whether your distances are in meters, masses in kilograms, and temperatures in kelvin. This is especially important with G, k, R, and σ because their units are less forgiving than something simple like g.

If you need a deeper process for that, review Dimensional Analysis in Physics: How to Check Equations and Catch Mistakes.

Use case 4: Matching constants to common course units

• Mechanics: g, G
• Electrostatics and E&M: k, e, ε₀, μ₀
• Waves and optics: c
• Modern physics: c, h, ħ, e, m_e, m_p
• Thermal physics: R, k_B, N_A, σ

This kind of grouping is useful if you are working through a broader College Physics 1 Study Guide or organizing a larger physics study guide for finals.

Use case 5: Studying smarter, not longer

If constants keep slowing you down, do not just reread them. Practice retrieval with short prompts:

• Which constant appears in photon energy?
• Which constant tells you weight near Earth?
• Which constant belongs in Coulomb’s law?
• Which constant connects moles to particles?

You can turn these into physics flashcards online or handwritten review cards. Then pair them with a few representative physics practice problems from each unit.

Use case 6: Knowing when outside help would save time

If your issue is not remembering values but choosing the right model, the problem is usually conceptual rather than memorization-based. In that case, a targeted review session or online physics tutoring guide can help you connect constants, formulas, and problem structure more efficiently than repeated guessing.

When to revisit

Come back to this page whenever your course shifts into a new unit, your formula sheet changes, or you notice the same constant-related mistakes repeating in homework and test corrections. A good reference page is most helpful at transition points.

Revisit this list when:

• You move from mechanics into electricity and magnetism
• You start AP Physics prep or cumulative final review
• You begin a modern physics chapter and suddenly see c, h, or e more often
• You are making a fresh formula sheet for an exam
• You keep confusing similar symbols like g and G, or k and k_B
• You need a quick check before doing physics exam practice sets

A practical update routine

1. Highlight the constants actually used in your current class unit.
2. Add one line under each constant: “used for...”
3. Write one sample equation beside each.
4. Mark any symbols that look similar and note the difference.
5. Test yourself without the sheet for two minutes.

If your larger goal is better exam performance, pair this routine with a structured plan such as Physics Final Exam Study Plan Template by Time Available or How to Improve Your Physics Grade: A Recovery Plan for the Next 30 Days.

The main idea is simple: a physics constants list is not just a chart of numbers. It is a map of the course. When you know what each constant means, where its units come from, and what kind of problem calls for it, you work faster and make better decisions. That is why this is the kind of reference page students return to throughout the year.