Decimal hours to hours and minutes: logbook conversion chart

How to convert decimal hours to hours and minutes

Keep the whole hours and multiply the decimal part by 60. 2.3 hours is 2 hours plus 0.3 × 60 = 18 minutes, so 2:18. 0.7 hours is 42 minutes. 12.45 hours is 12 hours plus 27 minutes, so 12:27.

To go the other way, divide the minutes by 60 and add the hours. 1:45 is 1 + 45 ÷ 60 = 1.75 hours. 0:50 is 0.833 hours, which is 0.8 to one decimal place. Only multiples of 6 minutes convert to an exact tenth: 0:06, 0:12, 0:18 and so on. Every other minute value needs a rounding decision.

Conversion chart: minutes to tenths and tenths to minutes

Tenths to minutes: 0.1 = 6, 0.2 = 12, 0.3 = 18, 0.4 = 24, 0.5 = 30, 0.6 = 36, 0.7 = 42, 0.8 = 48, 0.9 = 54, 1.0 = 60.

Minutes to the nearest tenth, with a 3-minute tie rounding up: 0 to 2 minutes = .0; 3 to 8 = .1; 9 to 14 = .2; 15 to 20 = .3; 21 to 26 = .4; 27 to 32 = .5; 33 to 38 = .6; 39 to 44 = .7; 45 to 50 = .8; 51 to 56 = .9; 57 to 60 = 1.0, which carries into the next hour. So 1:57 logs as 2.0 and 3:02 logs as 3.0.

If you round down instead, each band starts at its own tenth: 0 to 5 minutes = .0, 6 to 11 = .1, through 54 to 59 = .9.

Rounding rules pilots use

None of the logging rules read for this guide sets a rounding method: 14 CFR 61.51, EASA FCL.050 and its AMC, and CASR 61.345 say what to record and set no rounding method. Pilots who log decimals use one of two methods. Nearest tenth moves each entry by up to 3 minutes either way, and the errors cancel only when your flight lengths are spread evenly. Always rounding down loses up to 5 minutes a flight and never overstates your time.

The safest choice is not to round at all: record hours and minutes, and convert only when a form asks for decimals. Whichever method you use, use one method for every entry, because a logbook that rounds some flights up and some down has no rule an examiner or assessor can check it against.

Which format each authority's forms expect

FAA: Form 8710-1, the paper version of the application IACRA files, says in its instructions for the Record of Pilot Time that decimal points may be used as long as they are "legible". 61.51(b)(1)(ii) asks only for "Total flight time or lesson time" on each logbook entry, with no format.

EASA: the logbook layout in AMC1 FCL.050 says column 6, total time of flight, "may be entered in hours and minutes or decimal notation as desired", and that "All times should be in UTC". The example entries in the AMC are written in hours and minutes (2 15, 1 20, 9 40).

CASA: CASR 61.345(3) lists what you must record for each flight, including the flight time in each capacity, but sets no format. CASA's logbook page says "Logbooks may vary in layout and format" and that you can buy one, make your own or use an app.

How errors creep into totals

Rounding each line and adding the rounded figures drifts. Two hundred sectors of 1:03 add up to 210:00. Rounded to the nearest tenth, each is 1.1 (63 minutes sits on the 3-minute tie), and the column adds to 220.0, ten hours more than you flew. Two hundred sectors of 1:02 round to 1.0 each and add to 200.0 against an exact 206:40, so you lose 6.7 hours. Add totals from exact minutes and round only the final figure.

The other common error is mixing the two notations. 1:30 typed into a decimal column as 1.30 becomes 1 hour 18 minutes, 12 minutes short. Adding 1:45 and 1:30 on a calculator as 1.45 + 1.30 gives 2.75, when the total is 3:15, or 3.25 hours. This happens most when a pilot moves from a paper logbook kept in one notation to software set to the other. Near a licence threshold such as the 1,500 hours for an FAA ATP (61.159(a)), an EASA ATPL(A) (FCL.510.A(b)) or a CASA ATPL (61.705(1)), a few hours of drift decides whether you meet the minimum on paper.