ForHosting KIT · Developer Utilities

RAM latency calculator

Turn the CAS latency and clock on a memory kit into real time: CL16 at 1600 MHz, sold as DDR4-3200, takes 10 ns until the first word arrives. Kits with different cycles and speeds finally compare on one scale. Free in your browser.

  • Free
  • Runs in your browser
  • No sign-up
  • Your data stays on your device
Run — free How it works & API
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Run — free

Worked example

If you enter
Cas latency
16
Clock mhz
1,600
You get
Clock period ns
0.625
First word latency ns
10

True RAM latency is the time in nanoseconds until the first word of a DRAM burst becomes available after a column-address strobe. Module stickers and shopping pages advertise CAS latency as an integer clock-cycle count beside a clock speed in megahertz, and those two numbers hide the delay that actually governs responsiveness until you convert cycles into time.

What first-word RAM latency is and how CAS becomes nanoseconds

First-word RAM latency is the column-access delay: how many nanoseconds elapse between a valid column address and the first beat of data on the DQ bus. JEDEC timing sheets print that delay as CAS latency, an integer number of DRAM clock cycles, next to a clock frequency in megahertz. Cycles are not time.

Two kits with the same CL can feel different because their clocks differ; two kits with different CL can feel the same if the faster clock shortens the period enough to cancel the extra cycles. The conversion is a single division. The clock period tCK in nanoseconds is one thousand divided by the clock in megahertz, because one megahertz is one million cycles per second and one nanosecond is one billionth of a second.

Worked example: a DDR4 module whose command clock is 1600 MHz, marketed as DDR4-3200, with CL16 has tCK equal to 1000/1600 = 0.625 ns and first-word latency 16 × 0.625 = 10 ns. The same CL16 at a 2000 MHz clock, DDR4-4000, drops to 8 ns.

Input contract, DDR clock versus advertised data rate, and errors

Numeric strings are parsed. A missing or non-finite field fails the same way. CAS latency must be a non-negative finite number; a negative cycle count is rejected.

Values are rounded to twelve decimal places so goldens and clients compare stably across JavaScript runtimes. Important: advertised DDR names such as DDR4-3200 or DDR5-6000 are data rates in megatransfers per second, not the command clock. DDR transfers twice per clock, so the clock in megahertz is half the MT/s rating.

Enter 1600 for DDR4-3200 and 3000 for DDR5-6000.

Where a RAM latency calculator earns its keep

PC builders use a RAM latency calculator when two kits sit at similar prices and the store page only prints CL and a megahertz-style speed. Converting both to nanoseconds answers whether the tighter CAS on the slower kit actually wins. Overclockers and memory tuners run the same identity after each BIOS change: if you raise the clock and leave CL alone, first-word latency falls; if you loosen CL to keep the kit stable at a higher clock, you can see immediately whether the net nanoseconds improved.

System integrators and server buyers compare JEDEC bins and EXPO or XMP profiles without opening a spreadsheet. Review sites and affiliate tables generate a true-latency column from SPD dumps so readers are not misled by a raw CL number next to a marketing frequency. Failed validation does not consume balance.

Keep requests small, reject non-positive clocks at the edge, and you get reproducible first-word latency for shopping scripts, overclocking logs, and edge workers without standing up a datasheet parser of your own.

What you can do with it

Compare DIMM kits before you buy

Convert each kit's CAS latency and command clock into first-word nanoseconds so a tighter CL on a slower stick can be ranked against a looser CL on a faster one.

Tune XMP, EXPO, and manual timings

After each BIOS clock or CL change, recompute first-word latency and keep the profile only when the nanosecond figure actually improved.

Server and workstation JEDEC bins

Rank registered DIMM speed bins and JEDEC tables by true column-access time instead of by the advertised megatransfer rate alone.

FAQ

Should I enter DDR4-3200 as 3200 MHz or 1600 MHz?

Enter the command clock, not the advertised data rate. DDR transfers twice per clock, so DDR4-3200 is 1600 MHz and DDR5-6000 is 3000 MHz.

Is first-word latency the same as full random-access latency?

A full random access also waits through tRCD, tRP, tRAS and other bank timings that this calculator does not include.

How do I compare two RAM kits with different CL and speed?

Convert both to nanoseconds and compare those. CL16 at a 1600 MHz clock gives 10 ns, while the same CL16 at 2000 MHz, sold as DDR4-4000, gives 8 ns, so the second kit delivers its first word sooner.

Does a higher CAS number always mean slower memory?

No. CAS counts clock cycles, not time. A faster clock shortens each cycle, so a kit with more cycles can end up just as quick, or quicker, than a kit with fewer cycles on a slower clock.

What happens if I enter a clock speed of zero?

It is refused, along with any negative value. The length of one cycle is 1000 divided by the clock in megahertz, and that division has no meaning for zero or a negative number.

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For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/dev/ram-latency

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/dev/ram-latency \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"cas_latency":16,"clock_mhz":1600}'

Example request

{
  "cas_latency": 16,
  "clock_mhz": 1600
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "dev.ram_latency",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTPCodeMeaning
401unauthorizedMissing or invalid API key.
402insufficient_balanceYour balance doesn't cover the task price.
404unknown_typeThat task type doesn't exist.
429rate_limitedToo many requests. Use the webhook instead of polling.

Technical notes

This RAM latency calculator applies the first-word identity t_ns equals CAS times one thousand divided by the clock in megahertz, returning the column-access delay used to compare DIMM kits, XMP profiles, and JEDEC bins. Enter the CAS timing and a strictly positive DRAM clock in megahertz; a zero or negative clock is rejected as invalid_input because the period would be undefined.

What first-word RAM latency is and how CAS becomes nanoseconds

Multiplying that period by the CAS cycle count yields first-word latency tCL in nanoseconds: t_ns equals cas_latency times 1000 divided by clock_mhz. This endpoint returns both the period and the first-word time so you can audit the arithmetic, not only the headline nanosecond figure that comparison tables display.

Input contract, DDR clock versus advertised data rate, and errors

Send JSON with two required finite numbers: cas_latency, the CAS cycle count printed as CL on the module or in the SPD, and clock_mhz, the DRAM command clock in megahertz. Aliases cas, cl, and cas_cl are accepted for the cycle count; clock_speed, frequency, mhz, and clock are accepted for the clock. The clock must be strictly positive: a zero or negative frequency would make the period 1000/f undefined or negative, so the task fails with invalid_input naming clock_mhz and is not billed. On success the body echoes cas_latency and clock_mhz, returns clock_period_ns as tCK, returns first_word_latency_ns as the primary result, and restates the formula t_ns = cas_latency * 1000 / clock_mhz. If you paste 3200 as clock_mhz you will compute half the true first-word latency. This calculator does not fold in tRCD, tRP, tRAS, bank-group gaps, or command-to-command delays; those extra clocks belong to a full random-access path, not to first-word column latency.

Where a RAM latency calculator earns its keep

Firmware notes and bring-up scripts pin the rounded nanosecond fields in tests and document that clock_mhz is the command clock, not the DDR data rate.

Technical questions

How is first-word RAM latency calculated from CAS and clock speed?

First-word latency in nanoseconds is cas_latency × 1000 / clock_mhz, where cas_latency is CL in clock cycles and clock_mhz is the DRAM command clock in megahertz. The clock period tCK is 1000 / clock_mhz nanoseconds.

What happens if the clock speed is zero or negative?

The task fails with invalid_input. A non-positive clock speed makes the period undefined, so the calculator rejects it and the call is not billed.

What does the RAM latency calculator cost?

The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.

Read the full KIT documentation →