The Music Duration Calculator computes:

• Duration of Music based on it's tempo, time signature and number of bars
• Tempo of Music based on the duration, time signature and number of bars.

What is the use?

- If you are composing music, this could be useful for determining the length of your song. It is handy for recording or when performing.
- Determining how fast or slow you have to play a song is crucial for instances like playing a soundtrack over a video or playing a song for a limited slot time. 

Instructions

The calculator has two buttons.  One to compute Music Duration, and one to compute Music Temp.

To find the Music Duration, click on the Duration button enter the following: 

1. Tempo (for example: 112 bpm)
2.  Number of measures (this could be found by counting the amount of bars from sheet music perhaps).
3.  Number of beats per measure which is given by the top unit of the time signature.

             Example: Tempo = 100 bpm, number of measures = 140, beats per measure = 4 

            length of song = `(4 x 140)/100   *  (60 "seconds")/"minute"`  =  336 seconds or 5.6 minutes
                             

To find Music Tempo, click on the Tempo button enter the following:

1. Beats per measure
2. Number of measures
3. Length of the music segment

You'll just need to manipulate the inputs in relation to the tempo:

Tempo = beats per measure x number of measures  x  60 seconds
                       length of song (in seconds)                                  minute
 

Different Tempos:

From fastest to slowest, the common tempo markings are:

• Prestissimo — extremely fast (200 and above bpm)
• Vivacissimamente — adverb of vivacissimo, "very quickly and lively"
• Vivacissimo — very fast and lively
• Presto — very fast (168–200 bpm)
• Allegrissimo — very fast
• Vivo — lively and fast
• Vivace — lively and fast (≈140 bpm)
• Allegro — fast and bright or "march tempo" (120–168 bpm)
• Allegro moderato — moderately quick (112–124 bpm)
• Allegretto — moderately fast (but less so than allegro)
• Allegretto grazioso — moderately fast and gracefully
• Moderato — moderately (108–120 bpm)
• Moderato espressivo — moderately with expression
• Andantino — alternatively faster or slower than andante
• Andante — at a walking pace (76–108 bpm)
• Tranquillamente — adverb of tranquillo, "tranquilly"
• Tranquillo — tranquil
• Adagietto — rather slow (70–80 bpm)
• Adagio — slow and stately (literally, "at ease") (66–76 bpm)
• Grave — slow and solemn
• Larghetto — rather broadly (60–66 bpm)
• Largo — Very slow (40–60 bpm), like lento
• Lento — very slow (40–60 bpm)
• Largamente/Largo — "broadly", very slow (40 bpm and below)
• Larghissimo — very very slow (20 bpm and below)

Terms for tempo change:

Rallentando – gradually slowing down
Ritardando – holding back, becoming slower
Ritenuto – immediately slowing down
Accelerando or stringendo – gradually accelerating

Articulation Terms:

• Marcato — marching tempo "Stacotto-ish" Strong
• Misterioso - slightly slower than marcato
• Tempo comodo — at a comfortable speed
• Tempo giusto — at a consistent speed
• L'istesso tempo — at the same speed
• Non troppo — not too much (e.g. Allegro ma non troppo, "fast but not too much")
• Assai — rather, very, enough as is needed (e.g. Adagio assai)
• Con — with (e.g. Andante con moto, "at a walking pace with motion")
• Molto — much, very (e.g. Molto allegro)
• Poco — a little (e.g. Poco allegro)
• Quasi — as if (e.g. Più allegro quasi presto, "faster, as if presto")
• tempo di... — the speed of a ... (e.g. Tempo di valse (speed of a waltz), Tempo di marcia
(speed of a march)) 

Sources/References:
-http://pickuptheguitar.com/calculate-length-song
-http://www.signalcorpsbands.com/uploads/2/0/9/9/20995666/basic_tempo_markings.pdf

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