How this instrument works
An hour divides into 60 minutes, not 100, so a clock reading of '1:45' cannot simply be read as 1.45 hours — that misreads the 45 minutes as forty-five hundredths of an hour when it is actually 45⁄60, or 0.75. This calculator does the division for you, taking a separate Hours and Minutes entry and returning the single decimal figure that a billing system, spreadsheet or payroll platform actually expects to receive.
Law firms popularized decimal-hour billing well before most other industries, typically in increments of one tenth of an hour — six minutes — because a bill itemized to the minute reads as needlessly precise while a bill rounded to the quarter hour overcharges too easily on short tasks. A five-minute phone call becomes 0.1 hours billed, not 0.0833 repeating; an attorney's timesheet entry of 0h 15m converts here to exactly 0.25 decimal hours before that firm's practice-management software rounds it to its own billing increment.
Outside legal practice, payroll and timesheet platforms — ADP, Gusto, QuickBooks Time and similar systems — import decimal hours to calculate regular and overtime wages, since multiplying an hourly rate by a clock-format duration produces a wrong total the moment minutes enter the picture. A shift logged as 7 hours 45 minutes needs to reach payroll as 7.75, not 7.45 or 7:45, and getting that translation wrong across a batch of weekly timesheets compounds into a real payroll error rather than a rounding curiosity.
- Enter the whole-hour portion of your time into Hours; 1 is preloaded.
- Enter the leftover minutes, 0 to 59, into Minutes; 30 is preloaded to show a clean half-hour example.
- Read Decimal hours for the combined figure, shown to four decimal places and recalculated instantly.
- Billing in tenths of an hour? Round the Decimal hours result to one decimal place using your firm's convention — most round up past the midpoint of each six-minute increment.
Worked example — a 1h 30m deposition prep session
A paralegal logs 1 hour 30 minutes preparing exhibits ahead of a deposition. Entering 1 into Hours and 30 into Minutes returns 1.5 decimal hours — a figure that drops straight into the firm's billing software without needing to round, since 30 minutes is exactly half of 60 and already lands on a tenth-of-an-hour boundary.
A second task that same day runs 0 hours 15 minutes reviewing a short email chain, which converts to 0.25 decimal hours. Most tenth-of-an-hour billing conventions round that up to the nearest 0.1, giving 0.3 billed hours — an 18-minute charge for a 15-minute task, three extra minutes of coarsening that is exactly the kind of thing a client is entitled to see explained in the firm's billing policy.
Questions
Why is 1 hour 45 minutes not 1.45 decimal hours?
Because an hour splits into 60 minutes, not 100, so decimal hours are a base-60-to-base-10 conversion, not a straight relabeling of the clock figure. Forty-five minutes is 45 ÷ 60 = 0.75 of an hour, which makes 1 hour 45 minutes equal to 1.75 decimal hours. Treating the clock reading '1:45' as if it already were '1.45' overstates the true duration by a tenth of an hour on this example alone, and the error scales with however many such entries get summed.
Why do law firms bill in tenths of an hour instead of exact minutes?
Six-minute increments strike a practical balance: fine enough that clients aren't charged a full quarter-hour for a two-minute phone call, coarse enough that the billing software and the invoice itself stay legible instead of showing figures like 0.1833 hours. Most practice-management platforms convert logged minutes to decimal hours first, exactly as this calculator does, and only then round to the nearest 0.1 according to the firm's stated rounding rule.
Does decimal-hour rounding always favor the firm billing the time?
It depends on the convention chosen and is worth checking on any invoice. Some systems round up at any fraction of a six-minute block, which favors the biller; others round to the nearest block, splitting the difference; bar association ethics guidance in a number of jurisdictions expects rounding rules to be disclosed to clients rather than applied silently. This calculator returns the unrounded decimal figure specifically so that whatever rounding a firm applies afterward is visible as a separate, checkable step.
How do payroll systems use decimal hours differently than law firms do?
Payroll typically keeps the full decimal figure, or rounds only to the nearest hundredth, because wages are calculated by multiplying an hourly rate directly against however many decimal hours were worked — coarser rounding there would systematically over- or under-pay employees across a pay period. Legal billing's six-minute rounding exists for client-facing invoice readability, a concern payroll math doesn't share.
What's the fastest way to convert clock time to decimal hours by hand?
Divide the minutes by 60 and add the result to the whole hours: 20 minutes is 20 ÷ 60 = 0.3333, so 2 hours 20 minutes becomes 2.3333 decimal hours. A handful of minute counts are worth memorizing since they recur constantly — 15 minutes is 0.25, 30 is 0.5, 45 is 0.75 — which covers most quarter-hour-logged timesheets without needing a calculator at all.
Can minutes ever be entered as 60 or more in this calculator?
No — Minutes should stay between 0 and 59, with anything beyond an hour carried over into the Hours field instead, the same way a clock rolls over. A 1.5-hour task belongs in this calculator as Hours = 1, Minutes = 30, not Hours = 1, Minutes = 90; carrying the extra 30 minutes into the hours column first, the way a clock would, keeps the result correct.