Calculating your value in rem is straightforward once you know the PX to REM formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the PX to REM Calculator.
What is PX to REM?
The PX to REM calculation tells you your value in rem from a few simple inputs. The figure you are solving for here is the value in rem.
The PX to REM formula
The core formula is:
Value in rem = Pixels (px) ÷ Base font size (Pixels (px))Here is what each input means:
- Pixels (px) — a number. Example: 24.
- Base font size (px) — a number. Example: 16.
How to calculate it step by step
- Write down the pixels (px) (for example, 24).
- Write down the base font size (px) (for example, 16).
- Apply the formula above to get your value in rem.
- Double-check the result with the PX to REM Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Pixels (px) | 24 |
| Base font size (px) | 16 |
| Value in rem | 1.5000 |
With pixels (px) of 24 and base font size (px) of 16, the value in rem works out to 1.5000.
Example 2
With pixels (px) of 48 and base font size (px) of 16, the value in rem works out to 3.0000.
| Result | Value |
|---|---|
| Value in rem | 3.0000 |
Example 3
With pixels (px) of 12 and base font size (px) of 16, the value in rem works out to 0.7500.
| Result | Value |
|---|---|
| Value in rem | 0.7500 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the PX to REM Calculator does it instantly, for free, with the formula and a worked example built in.
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