Calculator inputs
Formula used
This calculator estimates torque from electrical power, speed, and user factors.
- Input power: P_in = V × I (watts)
- Output power: P_out = P_in × η (η = efficiency)
- Angular speed: ω = 2π × RPM / 60 (rad/s)
- Continuous torque: T = (P_out / ω) × gear (Nm)
- Working torque: T_work = T × impact
- Safe torque: T_safe = T_work × (1 − margin)
Important
Impact torque is a planning estimate. Real output depends on tool model, impact mechanism, battery sag, bit fit, and joint friction.
How to use this calculator
- Enter your battery voltage and a realistic average current.
- Use loaded RPM, not the no-load marketing number.
- Set efficiency to 75–90% for typical cordless tools.
- Pick an impact multiplier: 1.4–2.2 works well.
- Add speed loss when you expect binding or wet wood.
- Apply a safety margin for soft heads or brittle timber.
- Compare Safe torque with the suggested range.
- Download CSV/PDF after one calculation run.
Example data table
| Scenario | V | A | Loaded RPM | η% | Impact | Margin% | Safe torque (Nm) |
|---|---|---|---|---|---|---|---|
| Deck screws in pine, pre-drilled | 18 | 10 | 2400 | 82 | 1.6 | 10 | 7.39 |
| Lag bolts for raised bed corner braces | 18 | 14 | 1800 | 80 | 2.1 | 15 | 22.65 |
| Concrete anchors for trellis base plates | 20 | 16 | 1600 | 78 | 2.3 | 20 | 30.91 |
These examples show relative changes. Your tool’s real torque may differ.
Session log (latest 25)
Run a calculation with “Add to my session log” enabled.
Built for planning garden builds: beds, decks, trellises, frames.