Refresh Rate to Frame Time Calculator

Background.

A refresh rate and a frame time are the same fact stated twice. The hertz is an SI derived unit whose expression in base units is s⁻¹, so a panel running at 144 Hz simply has a period of 1 ÷ 144 seconds — 6.944 milliseconds — between one vertical blank and the next. That millisecond figure is the more useful of the two, because it is a budget: every frame your machine draws has to be finished inside it, and profilers report the cost of shadow maps, post-processing and physics in milliseconds, not in frames per second.

The reason frame time beats frame rate as a working unit is that frames per second is a reciprocal, and reciprocals compress at the top of the scale. Going from 30 to 60 fps buys 16.7 ms per frame; going from 120 to 144 fps buys only 1.4 ms. A change of "30 fps" means something completely different at each end of the range, which is why optimisation targets are set in milliseconds.

The third output on this page is the one people are usually surprised by. With hard V-Sync, a finished frame cannot be shown the moment it is ready — it has to wait for a vertical blanking boundary. Microsoft's DXGI documentation states the rule plainly: the SyncInterval parameter of Present is an integer, where 1 through 4 means synchronise presentation after the nth vertical blank. Because that count is a whole number, a renderer that misses its window by a fraction of a millisecond does not lose a fraction of its frame rate — it loses half of it. On the default inputs here a renderer taking 8 ms on a 144 Hz panel is only 1.06 ms over budget and could sustain 125 fps unsynchronised, yet V-Sync holds every frame for two intervals and delivers exactly 72.

The rate-basis option handles the other thing that catches people out: broadcast rates are not round. Recommendation ITU-R BT.709-6 lists picture rates of 60, 60/1.001, 30, 30/1.001, 50, 25, 24 and 24/1.001, and ITU-R BT.2020-2 carries the same 1.001 divisor into 120 Hz and 100 Hz UHD. Selecting the NTSC basis applies the exact divisor rather than the rounded 59.94 that most tools show, so 60 Hz becomes 59.940059940… Hz and a 16.6667 ms interval becomes 16.6833 ms. Over an hour that 0.0167 ms per frame is the entire reason drop-frame timecode exists.

What is refresh rate to frame time calculator?

Refresh rate is how many times per second a display redraws its image, measured in hertz. Frame time — also called the refresh interval or the frame budget — is the elapsed time between two consecutive refreshes, and it is simply the reciprocal: 1000 divided by the refresh rate gives milliseconds per frame. 60 Hz is 16.67 ms, 120 Hz is 8.33 ms, 144 Hz is 6.94 ms and 240 Hz is 4.17 ms.

The distinction between the display's frame time and the renderer's frame time matters. The first is fixed by the panel and is a deadline; the second is measured and is a cost. When the cost exceeds the deadline the frame is late, and what happens next depends on how presentation is synchronised: with tearing allowed the partial frame is shown immediately, and with hard V-Sync the frame waits for the next blanking boundary, which quantises the delivered frame rate into a staircase of the refresh rate divided by 1, 2, 3 and so on.

How to use this calculator.

1. 01Choose whether you are starting from the refresh rate in hertz or from a measured interval in milliseconds.
2. 02Enter the panel's refresh rate — 60, 120, 144, 240 — or the interval you measured, whichever matches your mode.
3. 03Leave the rate basis on "exactly as entered" for a computer display; switch to the 1.001 divisor for broadcast and film rates, where 60 means 59.940 and 24 means 23.976.
4. 04Enter your renderer's actual frame time in milliseconds, taken from a profiler or a frame-time overlay. Use the 99th-percentile figure rather than the average if you are investigating stutter.
5. 05Read the frame budget used and the headroom to see how close you are to the deadline, and the V-Sync locked frame rate to see what the staircase costs you when you miss it.

The formula.

The hertz is defined in SI as a reciprocal second, so period and frequency are exact reciprocals of one another: T = 1 ÷ f seconds, or T = 1000 ÷ f milliseconds. At 144 Hz that is 1000 ÷ 144 = 6.9444… ms, and inverting it returns 144 Hz exactly. The microsecond figure is the same number multiplied by 1000, and frames per minute is the rate multiplied by 60.

The broadcast basis divides the entered rate by exactly 1.001 before anything else happens. This is not an approximation of 59.94 — it is the value the standards themselves specify. ITU-R BT.709-6 item 5.5 lists picture rates as 60, 60/1.001, 30, 30/1.001, 50, 25, 24, 24/1.001, and ITU-R BT.2020-2 Table 2 lists 120, 120/1.001, 100, 60, 60/1.001, 50, 30, 30/1.001, 25, 24, 24/1.001. Sixty divided by 1.001 is 59.940059940059940… Hz, whose interval is 1000 × 1.001 ÷ 60 = 16.68333… ms.

The budget figures are straightforward subtraction and division. Headroom is the interval minus the render time and is deliberately allowed to go negative, because a negative headroom is the informative case: it is the number of milliseconds that must be found. Budget used is the render time divided by the interval, expressed as a percentage, so anything above 100 per cent means the renderer cannot keep pace with the panel. Uncapped frame rate is 1000 divided by the render time — what the machine would deliver with synchronisation switched off entirely.

The V-Sync figure is where the whole numbers bite. A frame can only be flipped to the screen on a blanking boundary, so it occupies a whole number of intervals: n = ⌈t ÷ T⌉, floored at 1 because even an instantly-rendered frame still waits for one boundary. The delivered rate is then f ÷ n. On a 60 Hz panel that produces the familiar 60, 30, 20, 15 staircase as the render time crosses 16.67, 33.3 and 50 ms; on a 144 Hz panel it is 144, 72, 48, 36. This models hard, double-buffered V-Sync only — triple buffering, frame pacing and variable-refresh displays each break the staircase differently, and Microsoft notes that variable-refresh operation actually requires tearing to be enabled.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute of Standards and Technology, Special Publication 811 (2008 edition), Guide for the Use of the International System of Units (SI), Table 3 — the 22 SI coherent derived units with special names: frequency → hertz (Hz), expression in terms of SI base units s⁻¹; note (d): 'The hertz is used only for periodic phenomena.'
2. [2]Recommendation ITU-R BT.709-6 (06/2015), Parameter values for the HDTV standards for production and international programme exchange — item 5.5 Picture rate (Hz): 60, 60/1.001, 30, 30/1.001, 50, 25, 24, 24/1.001.
3. [3]Recommendation ITU-R BT.2020-2 (10/2015), Parameter values for ultra-high definition television systems — Table 2, Picture temporal characteristics: frame frequency 120, 120/1.001, 100, 60, 60/1.001, 50, 30, 30/1.001, 25, 24, 24/1.001; scan mode progressive.
4. [4]Microsoft, IDXGISwapChain::Present (dxgi.h), Win32 API reference — SyncInterval is 'an integer that specifies how to synchronize presentation of a frame with the vertical blank': 0 = 'the presentation occurs immediately, there is no synchronization'; '1 through 4 — Synchronize presentation after the nth vertical blank'. Variable refresh rate displays section: 'It is a requirement of variable refresh rate displays that tearing is enabled.'