How do you calculate how long your labour was?

[membas#1]

i was 4 cm several days before i even had a contraction. so i count from when contractions started and i knew they were contractions. around 5pm i felt like something was maybe happening, i was having some weird cramping but it was very irregular and nothing worth timing and not painful. so if i count from there it would have been 10.5 hours til she was born. however i usually count from when contractions were established and regular and i knew something was up for sure--that was around 8pm so I typically say 7.5 hours from established contractions to birth. i pushed for less than 10 minutes, about 4-5 contractions worth.