Belt tension calculator
Tension a GT2 / GT3 belt by ear: pluck the free span like a guitar string and match a frequency. Set a target tension to get the note to tune to, or enter a measured frequency to read your current tension.
Positioning belts (3D printers, small CNC) usually run ~5–8 N (0.5–0.8 kgf).
Display
Tune to
81.6Hz
Target tension
6.0 N · 0.61 kgf
Half-step band
79.2–84.1 Hz
Summary
6.0 N on a 150 mm span → pluck ≈ 81.6 HzT = 4 × μ × L² × f², a plucked free span vibrates like a string.
Typical belt mass per metre
Approximate linear mass density for common belts. The frequency formula is exact, these constants are not, so override them from your belt’s datasheet (or weigh a known length) when you need precision.
| Belt | Mass / metre |
|---|---|
| GT2 6 mm | 10 g/m |
| GT2 9 mm | 13 g/m |
| GT3 9 mm | 15 g/m |
| GT3 15 mm | 22 g/m |
Frequently asked questions
How do I measure belt tension without a gauge?
Pluck the free span like a guitar string and read the pitch (frequency in Hz) with a phone tuner or spectrogram app, then enter it in Measure mode. A tensioned belt vibrates like a string, so tension T = 4 × μ × L² × f².
What tension should a GT2 belt have?
Positioning belts on 3D printers and small CNC machines usually run about 5–8 N (0.5–0.8 kgf). Too loose causes backlash and layer shifts; too tight overloads bearings and flexes the frame.
Where on the belt do I pluck?
Pluck the straight, unsupported section between the two nearest pulleys, away from any carriage or idler. A shorter span rings at a higher frequency for the same tension.
What is 'mass per metre' and why does it matter?
It is the belt's linear weight in grams per metre. The vibration frequency depends on it, so it must match your belt. The presets are typical figures, for accuracy, weigh a known length or use your belt's datasheet.
What's the difference between Target and Measure mode?
Target mode takes a tension you want and tells you the frequency to tune the pluck to. Measure mode takes a frequency you measured and tells you the tension you currently have.
Does span length change the target frequency?
Yes. For the same tension a longer free span rings lower and a shorter span rings higher, so always enter your actual span length between the pulleys.
Frequency f = (1 ÷ 2L) × √(T ÷ μ); tension T = 4 × μ × L² × f², with L the free span in metres and μ the belt mass per metre in kg/m. Pluck between the two nearest pulleys, away from any carriage.