555 astable frequency calculator
With RA at 1000 Ω, RB at 10000 Ω and C at 1 µF, a 555 astable has a timing term of 21000 Ω, RA plus twice RB. Enter the three parts and get the ideal oscillation frequency and period. Free in your browser.
- Free
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- No sign-up
- Your data stays on your device
Run — free
Worked example
- R1
- 1,000
- R2
- 10,000
- C
- 0.000001
- Frequency hz
- 68.6997638519
- Period s
- 0.0145560908
- Resistance term ohm
- 21,000
This 555 astable frequency calculator turns two timing resistors and one timing capacitor into an ideal oscillation frequency and period. The result is an ideal first estimate: real components, supply conditions, temperature, and timer tolerances can shift the frequency built on a bench.
Enter the component values in base units
Enter both resistances in ohms and the capacitance in farads. For example, 1 kilohm is 1000 ohms, 10 kilohms is 10000 ohms, 1 microfarad is 0.000001 farads, and 10 nanofarads is 0.00000001 farads. In the conventional astable connection, R1 runs from the positive supply to the discharge pin.
Every value must be finite and greater than zero. A zero resistor or capacitor does not describe the supported classic circuit and is rejected instead of producing an infinite or misleading result. Convert labeled component values before submitting them, and double-check capacitor prefixes because confusing nanofarads with microfarads changes the answer by a factor of one thousand.
Apply the ideal value to a real 555 design
Treat the calculated frequency as a nominal design value, not a promise about a physical board. The ideal equation assumes exact resistor and capacitor values, ideal one-third and two-thirds supply thresholds, negligible leakage, and instantaneous output transitions. Real resistors have tolerance and temperature coefficients, while timing capacitors—especially electrolytic parts—may have wider tolerance, leakage, aging, and voltage dependence.
The timer itself contributes threshold and discharge-transistor variation. For an LED flasher or an audible indicator, those shifts may be harmless. For a calibrated clock, frequency reference, or precision measurement, a crystal, oscillator module, or microcontroller timer is usually more appropriate.
Choose practical resistor values that respect the device datasheet, and verify that capacitor leakage is small compared with the timing current. Breadboard capacitance can matter at very small C values, while leakage can dominate very large resistance values. After calculating, select available component values, rerun the equation with their nominal ratings, and evaluate worst-case combinations using their tolerances.
Then measure the assembled waveform with an oscilloscope or frequency counter. Because the algorithm uses no network, randomness, or clock, identical valid inputs always produce identical results.
What you can do with it
Choose LED flasher timing
Estimate the blink frequency produced by available resistor and capacitor values before assembling a simple 555 astable circuit.
Design a tone generator
Compare component combinations for an approximate audible oscillation frequency used with a buzzer or speaker driver.
Check electronics exercises
Calculate a deterministic reference frequency and period for teaching materials, worksheets, and automated answer checking.
FAQ
Which units should I enter?
Convert kilohms, megohms, microfarads, and nanofarads before submitting values.
Why does the calculated frequency differ from my measured circuit?
Component tolerance, capacitor leakage, timer threshold variation, wiring capacitance, temperature, and supply conditions can all move the real frequency away from the ideal value.
Does this calculate duty cycle?
No. This focused capability returns oscillation frequency, period, and the combined resistance term. Use a broader astable timing calculator when high time, low time, or duty cycle is required.
Why does my result differ from a datasheet that uses 1.44?
Because 1.44 is a rounded form of one over ln 2. This calculator keeps ln 2 at full precision, so frequency and period stay consistent with each other; the gap with the 1.44 formula comes only from that rounding.
Is a 555 good enough for a precise clock?
For an LED flasher or a buzzer, the drift from real parts is usually harmless. For a calibrated clock, a frequency reference or a precision measurement, a crystal, an oscillator module or a microcontroller timer is usually the better choice.
Related tools
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
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/elec/ne555-frequency \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"r1":1000,"r2":10000,"c":0.000001}'const res = await fetch("https://api.kit.forhosting.com/elec/ne555-frequency", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"r1": 1000,
"r2": 10000,
"c": 0.000001
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/ne555-frequency",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"r1": 1000,
"r2": 10000,
"c": 0.000001
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/ne555-frequency", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"r1":1000,"r2":10000,"c":0.000001}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"r1":1000,"r2":10000,"c":0.000001}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/ne555-frequency", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"r1": 1000,
"r2": 10000,
"c": 0.000001
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.ne555_frequency",
"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
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Enter the component values in base units
This unit convention avoids hidden multipliers and makes API calls unambiguous. The aliases ra and rb are accepted for the resistors, and capacitance is accepted for C, which can make integrations match schematic notation. Numeric strings are accepted by the calculation core, although JSON numbers are clearer for most callers. The response echoes the combined resistance term rather than silently converting units, making input mistakes easier to identify during prototyping or automated testing.
Understand the equation and returned result
With ideal threshold levels at one third and two thirds of the supply voltage, the charging and discharging intervals contain the natural logarithm of two. Frequency is the reciprocal of that period. The two satisfy frequency times period equals approximately one, subject only to output rounding. This focused calculator does not return duty cycle or individual high and low times; it is designed for the specific task of finding the oscillation rate. This capability evaluates that relationship directly as f = 1 / (ln(2) × (R1 + 2R2) × C). Some datasheets and textbooks replace 1 / ln(2) with the rounded constant 1.44; using Math.LN2 here preserves a more precise and internally consistent relationship between frequency_hz and period_s. The response also includes resistance_term_ohm, which is R1 + 2R2, and a formula label suitable for displaying alongside the answer. If you need cycles per second, read frequency_hz. If you need the duration of one complete high-and-low cycle, read period_s.
Apply the ideal value to a real 555 design
The browser version is convenient for interactive component selection, while automated tools can call the API for $0.002 per successful item to evaluate bills of materials, generate lab exercises, or validate configuration data.
Technical questions
What formula does the calculator use?
It uses f = 1 / (ln(2) × (R1 + 2R2) × C), the ideal equation for the conventional two-resistor 555 astable circuit.
How much does an API calculation cost?
Each successful API item costs $0.002. You can also run the browser calculator locally without an API call.