Guides
Looking after your guitar: the complete guide
Strings, cleaning, humidity, setup: the routines that keep a guitar pleasant to play for years, and the ones best left to a luthier.
Guitar calculators: string tension, delay time, speaker impedance
Free calculators for guitarists: string tension by gauge, tuning and scale length, tempo to milliseconds for setting a delay, speaker impedance, Ohm's law, watts to dB, inch to mm conversions.
String tension
Pick the scale length, tuning and a preset string gauge set (or set each gauge by hand) to estimate the tension of every string.
| Open note | Gauge (thousandths of an inch) | Type | Tension (kg) | Tension (lb) | Feel |
|---|---|---|---|---|---|
| E2 | 7.9 | 17.5 | normal | ||
| A2 | 8.9 | 19.5 | normal | ||
| D3 | 8.3 | 18.4 | normal | ||
| G3 | 7.5 | 16.6 | normal | ||
| B3 | 7.0 | 15.4 | normal | ||
| E4 | 7.3 | 16.2 | normal | ||
| Total tension | 46.9 | 103.5 |
Estimated from D'Addario's published unit weights for plain steel and nickel wound strings. For phosphor bronze acoustic strings, expect a few percent of difference from these figures.
Tempo ↔ milliseconds
Tap repeatedly at the desired tempo: the average of the last 4 gaps sets the BPM.
| Note value | Duration (ms) |
|---|---|
| Whole note | 2,000.0 |
| Half note | 1,000.0 |
| Dotted half note | 1,500.0 |
| Quarter note | 500.0 |
| Dotted quarter note | 750.0 |
| Eighth note | 250.0 |
| Dotted eighth note | 375.0 |
| Eighth note triplet | 166.7 |
| Sixteenth note | 125.0 |
| Sixteenth note triplet | 83.3 |
From a duration in ms
| BPM if it's a quarter note | 120.0 |
|---|---|
| BPM if it's an eighth note | 60.0 |
Impedance and power
Speakers
4.00 ΩTotal impedance
| Speaker | Power share |
|---|---|
| 8 Ω | 50 % |
| 8 Ω | 50 % |
Parallel wiring: every speaker sees the same voltage, so power splits inversely to impedance (the lowest-Ω speaker gets the most power).
Tube amp: stick to the output impedance set on the amp. A slightly higher-than-rated load is barely tolerable; never use a lower load, and never run the amp without any load connected.
Solid-state amp: never go below the minimum impedance stated by the manufacturer, or you risk damaging the output stage.
Ohm's law
Enter two values among U, I, R and P: the other two are calculated automatically.
Watts → decibels
+3.0 dBGain
- ×2 = +3 dB
- ×10 = +10 dB
- Doubling perceived loudness ≈ +10 dB
Conversions
Inches ↔ millimetres
Gauge (thousandths of an inch ↔ mm)
Pounds ↔ kilograms
Fretboard radius
| Radius | mm |
|---|---|
| 7.25″ | 184.1 |
| 9.50″ | 241.3 |
| 12.00″ | 304.8 |
| 16.00″ | 406.4 |
Common scale lengths
| Scale length | mm |
|---|---|
| 25.5″ (Fender, Ibanez…) | 647.7 |
| 24.75″ (Gibson) | 628.7 |
| 25″ (PRS) | 635.0 |
| 24″ (Jaguar, Mustang) | 609.6 |
| 27″ (baritone) | 685.8 |
| 34″ (bass) | 863.6 |
| 30″ (short-scale bass) | 762.0 |
Common action height
| Height | Feel |
|---|---|
| 1.5 mm | ≈ 4/64″ |
| 2.0 mm | ≈ 5/64″ |
How to use the calculators
Each calculator is independent; pick the tab you need.
- String tension: enter the guitar’s scale length (25.5 inches for a Stratocaster or Telecaster, 24.75 for a Les Paul, 34 inches for most basses), the tuning, then the gauge string by string or a full set from 8-38 to 13-56 (plus bass sets). The result appears in kilograms or pounds per string and in total, with a light, normal or heavy marker.
- Tempo to milliseconds: enter the BPM and read the length of each note value (semibreve, minim, crotchet, quaver, dotted quaver, triplet, semiquaver). Useful for setting a delay, a tremolo or an LFO.
- Speaker impedance: add your speakers in series or parallel and read the resulting impedance, with a reminder of the rules for valve and solid-state amps.
- Ohm’s law and watts to dB: voltage, current, resistance and power; comparison of two power ratings in decibels.
- Conversions: inches to millimetres and back, gauge in thousandths of an inch to millimetres, pounds to kilograms, fretboard radius, action.
Guitarist’s tips
- Think in tension, not gauge. A 10-46 on a 24.75-inch scale is lighter than the same set on 25.5 inches. If you change guitars and the feel seems different, the calculator explains why and lets you get the same feel back.
- Balance the set. Look at the tension string by string: on many standard sets, the G string is noticeably tighter than its neighbours. A wound G or an intermediate gauge on that string can fix an imbalance that gets in the way when bending.
- Delay on the dotted quaver, tremolo on the quaver. For the Edge effect, set the delay to the dotted quaver and play even quavers. For a rhythmic tremolo, the quaver or semiquaver works better. The TC Electronic Flashback, reviewed on the site, has tap tempo that makes the maths optional, but the value in ms is still useful for a knob-only delay.
- Two 8-ohm speakers in parallel make 4 ohms, in series 16 ohms. Before plugging an extra cabinet into a valve amp, check that the total matches a position on the selector. Among the combos reviewed on the site, the Fender Blues Junior IV and the Marshall DSL20HR clearly label their available outputs.
- Change gauge, check the setup. Going from 9-42 to 11-49 adds several kilos of tension: the neck relief shifts and the action rises. The guitar care guide covers truss rod and action adjustment.
Limits and transparency
The tension calculation relies on the unit weights published by D’Addario for nickel (electric) strings and on the classic physics formula linking tension, vibrating length, frequency and mass. It is an estimate: phosphor bronze, stainless steel, hex- or round-core strings, or strings from other makers deviate by a few percent. The actual vibrating length also differs slightly from the nominal scale length because of bridge compensation.
The light/normal/heavy marker is indicative and reflects common usage on electric and acoustic guitars, not a manufacturer’s recommendation. Action and radius values are orders of magnitude.
The impedance calculator does not replace your amp’s manual: mismatch tolerances vary between manufacturers, and some valve heads tolerate none. When in doubt, the exact impedance is the only safe rule. The first amp guide explains the differences between valves and transistors.
Going further
- The online tuner to check your tuning after a gauge change.
- The metronome to find the tempo to enter in the delay calculator.
Frequently asked questions
Which string gauge for drop C tuning?
Dropping a whole tone loses roughly 20% of tension at the same gauge: a 10-46 set in drop C goes floppy and buzzes. The calculator shows that an 11-52 or 12-56 set brings the tension back close to a 10-46 in standard. Then check the nut, which may need adjusting for the thicker strings.
How do I set a delay to the tempo of the song?
Divide 60,000 by the tempo in BPM to get the length of a crotchet in milliseconds: at 120 BPM a crotchet lasts 500 ms, a quaver 250 ms and a dotted quaver 375 ms. The dotted quaver is the classic setting for rhythmic rock and pop delays. Enter the tempo in the calculator and copy the value to the pedal.
Can I plug a 16-ohm cabinet into an 8-ohm amp?
On a solid-state amp, yes: a higher impedance than the rated one is safe, the amp simply delivers a little less power. A lower impedance, on the other hand, can overheat it. On a valve amp, match the impedance selected on the output; a one-step mismatch is generally tolerated by manufacturers, but check the manual.
Is a 100 W amp twice as loud as a 50 W amp?
No. Doubling the power adds 3 dB, which the ear perceives as a little louder, not twice as loud. For a perceived doubling of volume you need about ten times the power, that is 10 dB. Speaker efficiency often matters more than the amp's wattage.
What action is considered normal?
On an electric guitar, an action of about 1.5 to 2 mm under the low E at the 12th fret and a little less under the high E is common; on an acoustic, expect around 2 to 2.5 mm on the bass side. These are reference points, not rules: playing style, gauge and neck relief all shift the ideal value.
Last updated: 11 September 2026
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