g-Force Calculators

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g-Force (also called relative centrifugal force, RCF) expresses the acceleration experienced in a centrifuge as a multiple of Earth's gravitational acceleration (g = 9.8 m/s²). It is the scientifically correct way to specify centrifuge speed for experimental reproducibility — unlike RPM, which depends on the rotor radius. Converting between RPM and RCF requires the rotor radius. g-Force determines what cellular and subcellular structures sediment — from whole cells at low RCF to ribosomes and protein aggregates at ultracentrifuge speeds.

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g-Force Formula

RCF (g) = 1.118 × 10⁻⁵ × r × N²

Where r = rotor radius in centimeters (cm) and N = speed in revolutions per minute (RPM).

Rearranged for RPM: N = √(RCF / (1.118 × 10⁻⁵ × r))

Worked Example

Rotor radius = 10 cm, speed = 5,000 RPM:
RCF = 1.118 × 10⁻⁵ × 10 × 5,000² = 1.118 × 10⁻⁵ × 10 × 25,000,000 = 2,795 × g

Why Use RCF Instead of RPM?

Two centrifuges running at the same RPM with different rotor radii produce different g-forces. A large-radius rotor at 3,000 RPM produces more g-force than a small-radius rotor at the same RPM. Specifying RCF ensures reproducibility across laboratories with different equipment.

Typical g-Forces for Cell Fractionation

  • 300–600 × g (5 min): Pellet whole cells from culture
  • 500–1,500 × g (10 min): Pellet cell debris and nuclei from homogenate
  • 3,000–5,000 × g (15 min): Pellet mitochondria (crude fraction)
  • 10,000–20,000 × g (20 min): Pellet lysosomes, peroxisomes, membrane vesicles
  • 100,000–200,000 × g (60–120 min, ultracentrifuge): Pellet ribosomes, large protein complexes, viruses
  • 300,000 × g+ (ultracentrifuge): Pellet small membrane fragments, polysomes

Blood Tube Centrifugation

  • Serum separation: 1,500–2,000 × g for 10 minutes
  • PRP (platelet-rich plasma): 200–400 × g for 10 minutes
  • Platelet-poor plasma: 2,000 × g for 10 minutes

Glossary

RCF (Relative Centrifugal Force)
Centrifugal acceleration expressed as a multiple of Earth's gravity (g = 9.8 m/s²). RCF = 1.118 × 10⁻⁵ × r × N². The correct way to specify centrifuge conditions for reproducibility across rotors.
RPM (Revolutions Per Minute)
Rotational speed of a centrifuge rotor. Does not specify centrifugal force without the rotor radius. Convert to RCF for reproducible reporting. RPM = √(RCF/(1.118 × 10⁻⁵ × r)).
Differential Centrifugation
Sequential centrifugation at increasing speeds to separate cellular fractions by sedimentation rate. Nuclei and debris pellet at low g; mitochondria at moderate g; ribosomes and membranes at high ultracentrifuge speeds.

Frequently Asked Questions

RCF = 1.118 × 10⁻⁵ × r × N², where r = rotor radius in cm and N = speed in RPM. Example: r = 15 cm, N = 4,000 RPM: RCF = 1.118 × 10⁻⁵ × 15 × 16,000,000 = 2,683 × g. Many centrifuges have a built-in RPM/RCF conversion button, or use nomograms and online calculators. Always specify g-force (RCF) in methods sections so others can reproduce your work with different rotors.

RPM tells you how fast the rotor spins but not the actual centrifugal force on the sample — which also depends on rotor radius. Larger rotors create more centrifugal force at the same RPM. Specifying RCF (× g) ensures that anyone reproducing your protocol achieves the same sedimentation force regardless of their rotor size. This is essential for reproducibility in published methods, especially for differential centrifugation procedures separating specific organelles.

Mitochondria are pelleted by differential centrifugation at approximately 3,000–10,000 × g for 10–15 minutes. A standard protocol for crude mitochondrial fraction: (1) homogenize cells in isotonic buffer; (2) low-speed spin 600 × g × 10 min (pellets nuclei, cell debris — discard); (3) 10,000 × g × 10 min (pellets mitochondria — keep); (4) 100,000 × g × 60 min (pellets microsomes from supernatant). The 10,000 × g pellet is the crude mitochondrial fraction.

A microcentrifuge (benchtop) spins 0.5–2 mL tubes at up to 20,000–25,000 × g. Used for pelleting bacteria, precipitating DNA/protein, clearing cell lysates, and routine molecular biology. An ultracentrifuge spins at 100,000–800,000 × g using vacuum-sealed, precision-balanced rotors. Used for pelleting ribosomes, viruses, membrane vesicles, and purifying macromolecular complexes. Ultracentrifuges require specialized equipment, special rotors, and run in vacuum to reduce rotor heating from air friction.