Physics constants and formulas: look up a value or solve for the unknown
Look up a physical constant by name or symbol and see its value, its unit and whether it is exact by definition or measured with an uncertainty. In each of the 17 physics formulas, leave one field empty and the calculator solves it in the unit you pick.
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- 17 constantsexact and measured, each labelled
- 17 formulasmechanics, electricity, heat, optics, gases
- Solve for the unknownthe empty field is calculated
- Unitskg or g, K or °C, Pa or atm
Physics constants by SI 2019
Physics constants and formulas is a free online tool from EduFacturing that puts 17 physical constants and 17 physics formulas from mechanics, electricity, heat, optics and gases in one place. The constants follow SI 2019 and NIST CODATA 2022, and every formula has a calculator that solves it for the unknown you choose.
What sets it apart from a plain table is the label. Each constant is defining, derived, exact by convention or measured. Exact ones carry no uncertainty because they are a definition or a product of definitions. Measured ones show the ± and its relative size. The calculation runs in your browser, with no request to a server.
Physics formula calculator
Shows 17 physical constants with a label
Seven are the SI 2019 defining constants (Δν_Cs, c, h, e, k, N_A, K_cd), three are derived (R, σ, F), one is exact by convention (g₀) and six are measured (G, α, m_e, m_p, ε₀, μ₀). The Constants view filters them by kind.
Solves 17 physics formulas for the unknown
Fill every field except the one you want and the calculator works out the empty one as you type. A unit menu sits next to the field, for example kg or g, K or °C, Pa or atm. For Ohm's law you give two of V, I, R and P and get the other two.
Shows the built-in constants
Seven formulas use a constant: Coulomb's law (ε₀), the Stefan-Boltzmann law (σ), the ideal gas law and gas density (R), the refractive index and λ·ν = c (c), and potential energy (g₀). The value is shown under the formula.
Searches by name or symbol
Type Boltzmann, G, Newton or Avogadro and get up to 10 matches across the constants and the formulas, by name or by symbol.
When you need a physics reference
A number without a unit and a source is half an answer.
Physics homework
A student solves a problem with F = m·a or P·V = n·R·T, leaves the unknown empty and checks the working.
A lesson on SI 2019
A teacher shows why the kilogram is no longer a standard in a vault but is defined through the Planck constant.
How units are converted
Everything is in SI: values are converted to base units, the formula is solved and the result is returned in the unit you chose.
To SI
A field accepts a number with a comma or a point. The value is multiplied by the unit's factor: 1 g = 10⁻³ kg, 1 atm = 101,325 Pa. Absolute temperature has an offset: K = °C + 273.15.
Solve
The formula is solved algebraically for the empty field. Cases with no solution are rejected with a message: division by zero, a negative mass or kinetic energy.
Result
The result is rounded to 10 significant digits and shown with up to 6 significant digits (5 in scientific notation), in the unit you chose.
| Applies to | Formula | Meaning |
|---|---|---|
| Kinetic energy | E_k = ½·m·v² | energy in J for mass in kg and speed in m/s |
| Coulomb's law | F = q₁·q₂ / (4π·ε₀·r²) | ε₀ is built in, charges are taken as absolute values |
| Stefan-Boltzmann law | P = σ·A·T⁴ | A in m², T in kelvin, σ = 5.670374419 × 10⁻⁸ W/(m²·K⁴) |
| Thin lens | 1/f = 1/s₁ + 1/s₂ | s₁ is object-lens, s₂ is lens-image |
| Ideal gas | P·V = n·R·T | R = 8.314462618 J/(mol·K) is built in |
What is different from a table
Units are inside the calculation
Mixing mm with m or g with kg does not spoil the result.
Values checked against NIST
The constants were checked on 1 August 2026 against NIST's allascii.txt table (CODATA 2022), with a note on each for why it is exact or where its uncertainty comes from.
The formulas are classical approximations, non-relativistic and non-quantum. E_k = ½·m·v² fails near the speed of light, the ideal gas law is not exact at very high pressure or very low temperature, and Coulomb's law is for point charges.
The adiabatic index γ is entered by hand, and Coulomb's law works with the absolute value of the charges. The list is chosen, not complete: the full CODATA table is on NIST's website.
Questions about physical constants
What is the Planck constant?
It is h = 6.62607015 × 10⁻³⁴ J·s, one of the seven defining constants of the SI since 2019. It is exact by definition, so there is no ± next to it, and the kilogram is defined through it.
Is there an Ohm's law calculator?
Yes. You give two of V, I, R and P and get the other two. Power can be shown in W, kW or MW.
What is the formula for kinetic energy?
E_k = ½·m·v²: energy in J for mass in kg and speed in m/s.
Why do the seven defining constants have no uncertainty?
Since 20 May 2019 seven constants are fixed with exact values and the units are derived from them: Δν_Cs, c, h, e, k, N_A and K_cd. They are not measured, so there is no ± next to them. R, F and σ are exact too: R = N_A·k, F = N_A·e, σ = 2π⁵k⁴ / (15·h³·c²), and the product or quotient of exact numbers is an exact number.
Why does the gravitational constant have such a large uncertainty?
Because G = 6.6743 × 10⁻¹¹ m³/(kg·s²) is the least precisely measured fundamental constant. Its relative uncertainty is about 2.2 × 10⁻⁵, more than 70,000 times that of the other five measured ones (1.5 to 3.1 × 10⁻¹⁰). CODATA 2022 repeats the 2018 value because there is no new data.
What changed for ε₀ and μ₀ in 2019?
Until then they were exact by definition: μ₀ = 4π × 10⁻⁷ N/A². After the redefinition the ampere no longer depends on that number, and μ₀ is derived from the measured fine-structure constant α, with its uncertainty. ε₀ is measured too.
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