labmatetools / 3.1 RPM ↔ g ALL TOOLS

RPM ↔ g Calculator

Protocols give spin speed in × g; centrifuges are often set in rpm. Enter your rotor radius and convert either way.

SECTION 03 — CONVERTERS · 3.1ENTER → CONVERT → SPIN

SOLVE FOR
rROTOR RADIUS
rpmSPEED
rpm
RCFRELATIVE FORCE
× g

Use the maximum radius — centre of the rotor to the bottom of the tube — from the rotor lid or the manual. Microcentrifuges are usually around 6–9 cm; benchtop swing-bucket rotors 10–20 cm.

ANSWER

SPIN
  1. ROTOR RADIUS—
  2. SET SPEED—
  3. FORCE—

MATCH ANOTHER CENTRIFUGEPROTOCOL IN RPM · USES YOUR r ABOVE

rpmPROTOCOL SPEED
rpm
rTHEIR ROTOR RADIUS
rpmSET YOURS TO
—

ABOUT THIS TOOL

How to use

  1. Enter your rotor radius in cm or mm. It is usually printed on the rotor or its lid, or listed in the centrifuge manual.
  2. Protocol says “spin at 12,000 × g”? Choose SOLVE FOR RPM and type 12000 in the force box.
  3. Centrifuge only shows rpm and you want to know the force? Choose SOLVE FOR × g.
  4. Protocol written in rpm for someone else's centrifuge? Use Match another centrifuge: enter their rpm and their rotor radius to get the rpm that gives the same force on yours.
  5. Many centrifuges can also be switched to show × g (RCF) directly — check the display settings.

The formula

RCF = 1.118 × 10⁻⁵ × r × rpm² rpm = √( RCF ÷ (1.118 × 10⁻⁵ × r) )
RCFrelative centrifugal force, in × g
rrotor radius in cm
rpmrevolutions per minute

Example. 12,000 × g with an 8.4 cm rotor: rpm = √(12000 ÷ (1.118 × 10⁻⁵ × 8.4)) ≈ 11,300 rpm.

Good to know

  1. Free to use. No subscription. Nothing you type leaves your browser.
  2. Force grows with the square of speed: double the rpm and you get four times the × g.
  3. Never run a rotor above its rated maximum speed, whatever the calculation says.
  4. Speeds are rounded to the nearest 10 rpm; forces to the nearest whole × g.
QUESTIONS · RPM TO G CALCULATOR

Frequently asked

What is the formula to convert rpm to g?

RCF = 1.118 × 10⁻⁵ × r × rpm², with r the rotor radius in cm. To go the other way, rpm = √(RCF ÷ (1.118 × 10⁻⁵ × r)).

Which rotor radius should I use?

The maximum radius — from the centre of the rotor to the bottom of the tube. It is usually printed on the rotor or lid, or in the manual. Microcentrifuges are around 6–9 cm.

How many rpm is 12,000 × g?

It depends on the rotor. With an 8.4 cm rotor, 12,000 × g is about 11,300 rpm.

A protocol gives rpm for a different centrifuge. What do I set?

Use Match another centrifuge: enter their rpm and their rotor radius to get the rpm that gives the same force on yours.