Measure from the same baseline
From the pencil line the sample was spotted on, measure to the centre of the spot and to the solvent front. Use one ruler and one unit for both — the calculator does not convert between them.
Calcolatore RF Cromatografia
Calcola il fattore di ritenzione (Rf) per la cromatografia su carta o strato sottile. Strumento di analisi chimica preciso per studenti e ricercatori.
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Calculate an Rf value
Enter both distances measured from the same baseline and the retention factor appears as you type. The division runs in your browser — no AI model, no upload, nothing saved.
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The Rf value formula
Rf = distance travelled by the spot / distance travelled by the solvent front
Measure both distances from the same baseline where the sample was spotted. Measure the spot to its centre and the solvent front to the line reached before the plate was removed.
Example: a spot travels 3.6 cm and the solvent front travels 8.0 cm. Rf = 3.6 / 8.0 = 0.45. Rf has no units and normally falls between 0 and 1. A value above 1 usually means the distances were measured from different reference points or entered incorrectly.
What an Rf value tells you
Rf describes how far a compound moves relative to the solvent under one specific set of conditions. A low Rf means the compound interacts more strongly with the stationary phase and moves less; a high Rf means it travels further with the mobile phase.
Compare Rf values only when the stationary phase, solvent system, temperature and run conditions are the same. Similar Rf values can support a comparison, but an Rf value alone does not identify an unknown compound.
How to use the Rf calculator
Enter both distances and pick the unit
Type the spot distance and the solvent-front distance, then choose cm, mm or in for both fields. The solvent front must be greater than 0 and the spot distance 0 or more.
Read the Rf value and the working
The retention factor appears as you type, with the formula, the numbers substituted into it and a reminder that Rf has no units. A spot measured beyond the solvent front is flagged instead of being reported as a valid Rf.
Come funziona
- Inserisci la distanza percorsa dal soluto.
- Inserisci la distanza percorsa dal solvente.
- Clicca su "Calcola Rf".
- Ottieni il valore del fattore di ritenzione per la tua analisi cromatografica.
Rf value calculator examples
Every example below is computed by the same code the calculator runs, so the substitution and the answer match exactly what you get when you type your own measurements in.
Example 1: A mid-range Rf
The spot travels 3.6 cm and the solvent front travels 8.0 cm on the same plate.
- Formula
- Rf = distance travelled by the spot / distance travelled by the solvent front
- Given
- spot = 3.6 cm, solvent front = 8.0 cm
- Calculation
- 3.6 ÷ 8.0 = 0.45
- Answer
- Rf value: 0.45 — Rf has no units.
Example 2: A low Rf
A polar compound holds on to the stationary phase and moves 2.4 cm while the solvent front reaches 9.6 cm.
- Formula
- Rf = distance travelled by the spot / distance travelled by the solvent front
- Given
- spot = 2.4 cm, solvent front = 9.6 cm
- Calculation
- 2.4 ÷ 9.6 = 0.25
- Answer
- Rf value: 0.25 — Rf has no units.
Example 3: A high Rf, measured in millimetres
Measured in millimetres instead: the spot travels 72 mm and the solvent front 90 mm. The unit cancels either way.
- Formula
- Rf = distance travelled by the spot / distance travelled by the solvent front
- Given
- spot = 72 mm, solvent front = 90 mm
- Calculation
- 72 ÷ 90 = 0.80
- Answer
- Rf value: 0.80 — Rf has no units.
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Frequently Asked Questions
How do you calculate an Rf value?
Divide the distance the spot travelled by the distance the solvent front travelled, measuring both from the same baseline. A spot travelling 3.6 cm with an 8.0 cm solvent front has an Rf of 0.45.
Can an Rf value be greater than 1?
No. The spot cannot normally travel farther than the solvent front, so Rf lies between 0 and 1. A value above 1 usually means the distances were measured from different reference points or entered incorrectly.
Does an Rf value have units?
No. Rf is a ratio of two distances, so the units cancel. Measure both distances in the same unit.
Why do Rf values differ between experiments?
Rf depends on the stationary phase, solvent system, temperature and how the plate was run. Compare values only under matching conditions.
What does a high or low Rf value mean?
A low Rf means the compound moved relatively little; a high Rf means it travelled farther with the solvent. Interpret it together with the stationary phase and solvent system.