How many times a day does every 3 hours run?

Eight times — 24 hours divided by a 3-hour step gives exactly 8 evenly-spaced runs, starting at midnight.

Is 0 */3 * * * the same as 0 0,3,6,9,12,15,18,21 * * *?

Yes, functionally identical — the step syntax is shorthand for that exact explicit list.

How do I restrict every-3-hours to daytime only?

Add an hour range before the step: 0 6-21/3 * * * only fires between 6 AM and 9 PM, still spaced 3 hours apart within that window.

Cron: Every 3 Hours

0 */3 * * * fires eight times a day — 00:00, 03:00, 06:00, and onward through 21:00. Since 3 evenly divides 24, the interval is perfectly consistent around the clock, making it a clean choice for moderate-frequency jobs that don't need to run every hour or two.

0 */3 * * *

Try it in Cron Parser

Examples & Variations

0 */3 * * *

Every 3 hours, all day

Try it

0 6-21/3 * * *

Every 3 hours, 6 AM–9 PM only

Try it

0 0,3,6,9,12,15,18,21 * * *

Same schedule, written as an explicit list

Try it

Common Mistakes

Writing an uneven step (like */5 in the hour field) expecting the same clean behavior — 5 doesn't divide 24, so it would produce an inconsistent, shrinking cycle the same way */45 does in minutes.
Not accounting for eight daily invocations when estimating API usage or costs — three-hour polling adds up faster than it sounds over a month.
Assuming this interval is 'business hours friendly' by default — it runs overnight too unless you explicitly restrict the hour range.

Best Practices

Good default for periodic reports, moderate-cost external API polling, or refreshing data that doesn't change minute-to-minute.
Use the explicit list form (0,3,6,9,...) if you want the schedule to be immediately readable without mental math, at the cost of a longer expression.
Pair with monitoring if a missed run matters — at only 8 runs a day, a single silent failure represents a meaningful gap in coverage.

Frequently Asked Questions

How many times a day does every 3 hours run?: Eight times — 24 hours divided by a 3-hour step gives exactly 8 evenly-spaced runs, starting at midnight.
Is 0 */3 * * * the same as 0 0,3,6,9,12,15,18,21 * * *?: Yes, functionally identical — the step syntax is shorthand for that exact explicit list.
How do I restrict every-3-hours to daytime only?: Add an hour range before the step: 0 6-21/3 * * * only fires between 6 AM and 9 PM, still spaced 3 hours apart within that window.

Related Tools

Cron Parser

Translate cron expressions to plain English

Cron Cheat Sheet

Quick reference for cron syntax, special characters, and shortcuts

Cron Examples Library

Browse and search common cron expression examples

Cron: Every 2 Hours

The cron expression for every 2 hours is 0 */2 * * *, firing at midnight, 2 AM, 4 AM, and so on. See examples, mistakes, and best practices.

Cron: Every 4 Hours

The cron expression for every 4 hours is 0 */4 * * *, firing 6 times a day. See examples, mistakes, and best practices for this schedule.

Cron: Every 6 Hours

The cron expression for every 6 hours is 0 */6 * * *, firing 4 times a day. See examples, mistakes, and best practices for this schedule.