Atomic Radius of Different Elements in Picometers (pm)
A complete guide to understanding atomic radii measured in picometers, including a reference list of common elements like Hydrogen, Carbon, and Oxygen.
Read articleNanometers to Millimeters Converter
Convert Nanometers (nm) to Millimeters (mm) — instantly, with scientific notation and nearest atomic-scale context.
Last updated:
How it works
Step 1: Enter the number you are stuck on
Type the exact value from your homework or lab report. No need to move decimal places in your head.
Step 2: Tell us your units
Select what unit you are starting with (like picometers or ångströms) and what unit you desperately need it to be in.
Step 3: Get your answer instantly
We give you the converted number, scientific notation in metres, and a real-world atomic scale context so you know your answer makes sense.
How the Math Actually Works
When you are dealing with numbers like 10⁻¹², the margin for error is brutal. A picometer is exactly one trillionth of a metre. The easiest way to avoid slipping up is to anchor everything to the metre. Don't try to memorize direct conversions for every possible pairing. The trick is simple: Convert whatever weird unit you have into metres first. Then, divide by the factor of the unit you want. Here are the only numbers you really need to memorize to survive chemistry: - **1 nm = 1,000 pm** - **1 Å = 100 pm** - **1 µm = 1,000,000 pm**
Convert A → B:
Step 1: Value (m) = Value × (metres per unit A)
Step 2: Result = Value (m) ÷ (metres per unit B)Example
Let's look at the numbers for a C–C bond length of 154 pm. Converting to nanometers? Step 1: 154 × 10⁻¹² = 1.54×10⁻¹⁰ m. Step 2: 1.54×10⁻¹⁰ ÷ 10⁻⁹ = 0.154 nm. You just successfully converted to nanometers without sweating the decimals.
Worked examples
| Scenario | Calculation | Result |
|---|---|---|
| Hydrogen atom radius (53 pm) → Å and nm | 53 × 10⁻¹² m ÷ 10⁻¹⁰ (Å); ÷ 10⁻⁹ (nm) | 0.53 Å · 0.053 nm |
| Carbon–carbon bond (154 pm) → nm | 154 × 10⁻¹² m ÷ 10⁻⁹ | 0.154 nm (1.54 Å) |
| X-ray wavelength (100 pm) → nm | 100 × 10⁻¹² m ÷ 10⁻⁹ | 0.1 nm (1 Å) |
| Visible light (500 nm) → pm | 500 × 10⁻⁹ m ÷ 10⁻¹² | 500,000 pm (5,000 Å) |
| DNA helix width (2 nm) → pm | 2 × 10⁻⁹ m ÷ 10⁻¹² | 2,000 pm (20 Å) |
Conversion reference
| Picometers (pm) | Femtometers (fm) | Ångströms (Å) | Nanometers (nm) | Meters (m) |
|---|---|---|---|---|
| 1 | 1,000 | 0.01 | 0.001 | 1×10⁻¹² |
| 10 | 10,000 | 0.1 | 0.01 | 1×10⁻¹¹ |
| 100 | 100,000 | 1 | 0.1 | 1×10⁻¹⁰ |
| 1,000 | 1,000,000 | 10 | 1 | 1×10⁻⁹ |
| 10,000 | 10,000,000 | 100 | 10 | 1×10⁻⁸ |
| 100,000 | 100,000,000 | 1,000 | 100 | 1×10⁻⁷ |
| 1,000,000 | 1,000,000,000 | 10,000 | 1,000 | 1×10⁻⁶ |
| 1×10⁹ | 1×10¹² | 10,000,000 | 1,000,000 | 0.001 |
| 1×10¹² | 1×10¹⁵ | 1×10¹⁰ | 1,000,000,000 | 1 |
Quick facts
- 1 pm = 10⁻¹² m. It is exactly one trillionth of a metre.
- A hydrogen atom radius is roughly 53 pm.
- 1 ångström = 100 pm = 0.1 nm. Always remember this for reading older journal papers.
- A typical covalent bond falls between 74 pm and 250 pm.
- Hard X-rays have wavelengths of 10–100 pm. That is why they can see crystal structures.
From the blog
View all →Frequently asked questions
To convert Nanometers to Millimeters, you can use our free online converter above. Simply enter the value in Nanometers and the calculator will instantly provide the equivalent value in Millimeters, complete with scientific notation and atomic-scale references.
We throw this word around a lot, but a picometer (pm) is simply 10⁻¹² metres. It is one trillionth of a metre. You use it because at the atomic scale, writing decimals with twelve zeros is a nightmare. It is the perfect scale for atomic radii and chemical bond lengths.
The problem with small metric units is losing track of the zeros. Think of it this way: there are exactly **1,000 picometers in one nanometer**. To go from nm to pm, just multiply by 1,000. It is that simple.
The ångström (Å) equals exactly 100 picometers. It is not an official SI unit, but crystallographers have used it for decades and refuse to stop. If you see 1.54 Å in a textbook, just multiply by 100 to get 154 pm.
Hydrogen, the smallest atom, has a radius of about 53 pm. Larger atoms like carbon sit at roughly 77 pm. The biggest atoms barely scratch 300 pm. So if you are calculating atomic size and get something like 5,000 pm, check your math.
The femtometer (fm) is 10⁻¹⁵ m. You only use femtometers when you are diving into the atomic nucleus itself, which is a fraction of a picometer wide.