# What is the Rf value?

Finds the retention factor (Rf) of a spot in thin-layer or paper chromatography: the distance the spot moved divided by the distance the solvent front moved, or either distance from the other and the Rf.

- Page: https://www.acalculator.org/chemistry/rf-value-calculator
- JSON spec: https://www.acalculator.org/chemistry/rf-value-calculator.json
- Version: 49c6b8530f82

## Default answer

Example with the default inputs (Find Rf, Distance the spot moved 22 mm, Distance the solvent front moved 40 mm): Rf = 0.55: the spot moved 55% as far as the solvent front.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| find | Find | Which value to work out: the Rf, the spot’s distance, or the solvent front’s distance. |
| d | Distance the spot moved | From the baseline (where the sample was put) to the middle of the spot. |
| f | Distance the solvent front moved | From the baseline to the solvent front, marked when the plate was taken out. |
| rf | Rf value | The retention factor, from 0 (the spot stayed on the baseline) to 1 (it moved with the front). |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| result | Answer | The Rf to 2 decimals, or the distance worked out in mm and cm. |
| rfValue | Rf (full) | The retention factor to 6 significant figures. |
| percent | Share of the front’s distance (%) | How far the spot moved, as a percent of the front’s distance. |
| spotMm | Spot distance (mm) | The distance from the baseline to the middle of the spot, in millimeters. |
| frontMm | Front distance (mm) | The distance from the baseline to the solvent front, in millimeters. |

## Method

Rf = distance the spot moved ÷ distance the solvent front moved, both measured from the baseline; spot distance = Rf × front distance; front distance = spot distance ÷ Rf.

## Assumptions

- Both distances are measured from the baseline (origin) on the same plate: to the middle of the spot and to the solvent front.
- The spot cannot move past the front, so the Rf is from 0 to 1. The Rf is shown to 2 decimals, rounded half up from its exact value.

## Worked examples

1. find = rf, d = 0.022, f = 0.04 gives result = Rf = 0.55, rfValue = 0.55, percent = 55. Source: LibreTexts, Nichols, Organic Chemistry Lab Techniques, §2.3C The Retention Factor (Rf = distance traveled by the compound ÷ distance traveled by the solvent front), https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_(Nichols)/02%3A_Chromatography/2.03%3A_Thin_Layer_Chromatography_(TLC)/2.3C%3A_The_Retention_Factor, Figure 2.14a: 22 mm ÷ 40 mm = 0.55.
2. find = rf, d = 0.0069, f = 0.02 gives result = Rf = 0.35, rfValue = 0.345.
3. find = spot, rf = 0.35, f = 0.05 gives spotMm = 17.5, result = Spot distance = 17.5 mm (1.75 cm). Source: LibreTexts, Nichols, Organic Chemistry Lab Techniques, §2.3C The Retention Factor (Rf = distance traveled by the compound ÷ distance traveled by the solvent front), https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_(Nichols)/02%3A_Chromatography/2.03%3A_Thin_Layer_Chromatography_(TLC)/2.3C%3A_The_Retention_Factor (Rf formula).
4. find = front, rf = 0.55, d = 0.033 gives frontMm = 60, result = Solvent front distance = 60 mm (6 cm). Source: LibreTexts, Nichols, Organic Chemistry Lab Techniques, §2.3C The Retention Factor (Rf = distance traveled by the compound ÷ distance traveled by the solvent front), https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_(Nichols)/02%3A_Chromatography/2.03%3A_Thin_Layer_Chromatography_(TLC)/2.3C%3A_The_Retention_Factor (Rf formula).

## FAQ

### How do I calculate an Rf value?

Measure two distances from the baseline (where you put the sample): to the middle of the spot, and to the solvent front. Divide the first by the second. A spot 22 mm from the baseline with the front at 40 mm has Rf = 22 ÷ 40 = 0.55.

### What does an Rf of 0.55 mean?

The spot moved 55% as far as the solvent front. An Rf near 0 means the compound stayed near the baseline (it holds on to the plate); an Rf near 1 means it moved almost as far as the solvent.

### Why is the Rf always between 0 and 1?

The compound is carried by the solvent, so its spot cannot move farther than the solvent front. The page refuses a spot distance larger than the front’s distance.

### Does the Rf value have units?

No. It is a ratio of two lengths, so the units cancel. Measure both distances in the same unit (millimeters are usual); the page also takes centimeters and inches and converts them.

### Where exactly do I measure to?

To the approximate middle of the spot, and to the solvent front. Mark the front in pencil as soon as you take the plate out of the chamber, because the solvent evaporates quickly and the front line disappears.

### Why do I get a slightly different Rf each time?

Rf values depend on the plate, the solvent mixture, the temperature and how far the solvent runs, so they are approximate. Nichols reports acetophenone runs in one solvent at 0.33, 0.38, 0.35 and 0.37. Compare a sample with a known compound on the same plate.

## Sources

- LibreTexts, Lisa Nichols (Butte College), Organic Chemistry Lab Techniques, §2.3C The Retention Factor (CC BY-NC-ND 4.0): Rf = distance traveled by the compound ÷ distance traveled by the solvent front, both measured from the baseline, the 22 mm ÷ 40 mm = 0.55 example (Figure 2.14a), the repeated acetophenone runs (Figure 2.15), and that Rf values are approximate. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_(Nichols)/02%3A_Chromatography/2.03%3A_Thin_Layer_Chromatography_(TLC)/2.3C%3A_The_Retention_Factor (retrieved 2026-10-19)