Per hour

How it works

How it works is division by a duration of one hour. The hour is 60 minutes or 3,600 seconds. The count is whatever you are measuring: items, kilometres, words, requests, currency units. Per hour means that count, divided by that duration. 12 per hour is 12 of the thing in 60 minutes. It is not 12 o’clock, and it is not a 12-hour span. The slash is a rate sign, not a date sign.

Write the thing, then the slash, then the hour unit. km/h is kilometres per hour. words/h is words per hour. 1/h is once per hour. h⁻¹ is the same once-per-hour in a style that puts the unit in the exponent. “Hourly” as an adverb is the prose form of the same rate when the count is one event: an hourly chime is 1/h. “Hourly” as a wage adjective means the pay rate uses the hour as the divisor. The grammar changes. The division does not.

A duration of one hour is PT1H, 60 min, or 3,600 s. A rate of 12 per hour is 12 / PT1H, which no one writes that way in a UI. They write 12/h. Mixing a duration format into a rate field is how 12:00 becomes twelve per hour in one reader’s eyes and noon in another’s. Keep rates in /h, /min, or /s. Keep clock stamps in hh:mm. Keep durations in h, min, s, or PT… strings.

12 per hour = 12/h = 12 hourly of that count 12 per hour = 0.2 per minute (12 ÷ 60) 12 per hour = 12/3,600 per second 1 per second = 3,600 per hour 1 per minute = 60 per hour

/h, hourly, and the inverse hour

The SI-friendly writing is the count, a slash, and h. Some forms want “per hour” spelled out. Some want “an hour.” Some want “hourly.” 60 km/h, 60 kilometres per hour, and 60 kilometres an hour are one rate. 60 kmh without the slash is a smashed format that people still parse as km/h; it is easier to misread as a code. Prefer the slash or the words.

h⁻¹ is “per hour” with no count in front: a frequency. 24 h⁻¹ is 24 per hour. That is not 24 hours. 24 h is the duration on the 24-hour page. 24/h is a rate that would finish 24 of the thing in one hour. The inverse unit does not turn a length into a speed by itself. You still need the count in the numerator.

Per hour is a rate. An hour is a sitting time. Writing both as “10” is how a speed becomes a nap, or a nap becomes a quota.

Per minute and per day from the same rate

To go down to per minute, divide the per-hour count by 60. 120 per hour is 2 per minute. To go down to per second, divide by 3,600. 3,600 per hour is 1 per second. To go up to per day, multiply by the hours in the day you mean. An ordinary 24-hour day gives × 24. A work day of 8 hours gives × 8 if the rate only runs while work runs. Do not multiply a waking rate by 24 and call it a daily total unless the thing truly runs all day.

Words per minute and words per hour are the same kind of rate on two divisors. 60 words per minute is 3,600 words per hour if that pace holds for 60 minutes. It often does not; the conversion is still the factor of 60, and the honesty is whether the pace holds. Currency per hour to currency per minute is ÷ 60. Kilometres per hour to metres per second is a different factor: 1 km/h = 1,000 m / 3,600 s. Name both units before you multiply.

Do not drop “per” and leave “hour.” “10 hour” is a duration. “10 per hour” is a rate. “10 hours” is a longer duration. “10/10:00” is a smashed clock. If a form has one box, label it rate or duration. If it has two boxes, put the count in one and the unit “per hour” in the other. The format is the whole phrase, not the numeral.