🔊 Decibel (dB) Calculator
The complete decibel reference — calculators, gain chain analysis, reference tables, SPL guide, and a ground-up explanation of why dB matters in electronics and audio.
Voltage Ratio ↔ dB
Power Ratio ↔ dB
dB → Voltage & Power Ratio
dBm Calculator
System Gain Chain — Add dB values in cascade
Enter the gain or loss (in dB) of each stage. Negative = loss/attenuation. The system total is simply their sum.
New to this? Here's what a gain chain is (tap to expand)
Real systems aren't one part — they're a chain of stages a signal passes through in order. An RF receiver, for example: antenna → amplifier → cable → another amplifier → filter. Each stage either boosts the signal (gain) or weakens it (loss). This tool answers the everyday question: after the signal passes through everything, how much stronger or weaker is it?
Here's the trick that makes dB so useful: because every stage is in dB, you don't multiply — you just add the numbers up. Gains are positive, losses are negative, and the total is the sum:
That same chain in raw ratios would mean multiplying ×100 × ×0.5 × ×200 × ×0.25 — messy arithmetic with unwieldy numbers. In dB it collapses to grade-school addition you can do in your head.
Why does adding work? Because a decibel is a logarithm, and logarithms turn multiplication into addition. Think of dB as steps on a staircase rather than “times bigger”: a gain is steps up, a loss is steps down, and the total is just where you end up — you count and add steps, you don't multiply them. That single property is the whole reason RF and audio engineers work in dB: every amplifier, cable, splitter, and connector becomes one number you add or subtract as you walk down the signal path.
Try it below: each stage you add or edit changes the running total instantly — watch the dB values simply sum.
Convert Any Power to dBm (and back)
dBm is power referenced to 1 milliwatt: 0 dBm = 1 mW exactly. Pick your unit from the dropdown — pW, nW, µW, mW, W, or kW — and it converts instantly. Try 1 mW → 0 dBm, 100 mW → 20 dBm, 1 W → 30 dBm.
| Power | dBm | Typical context |
|---|
A visual scale of the most important dB reference points every engineer should know by heart. The bar runs from heavy attenuation (left) through unity gain to strong amplification (right).
| dB Value | Voltage Ratio | Power Ratio | Meaning / Memory Hook | Visual |
|---|
Voltage vs Power — Why the 20/10 Difference?
Power is proportional to voltage squared (P = V²/R). So doubling voltage quadruples power. The factor-of-2 in the exponent becomes the factor-of-2 difference between the formulas:
Both give the same dB number when measured across equal impedances. The 20 absorbs the squaring.
The Three Rules You Must Memorise
These three facts let you do dB arithmetic in your head:
Memorise these three. Any other dB value can be built by adding them. 26 dB = 20 + 6 = ×10 (power) × ×4 (power) = ×400 power.
dBm — Power Referenced to 1 mW
dBm pins the reference: 0 dBm = 1 mW. This makes it an absolute power measurement, not just a ratio. RF engineers live in dBm because it survives calculation chains:
Common levels: phone transmitter ~30 dBm (1 W); Wi-Fi AP ~20 dBm (100 mW); received Wi-Fi signal ~ −70 dBm (0.0000001 mW).
dBV, dBu, dBFS — The Audio References
Audio engineering uses different zero references:
Professional line level is +4 dBu; consumer is −10 dBV. Mix these references and you get a 12 dB level mismatch.
| dBm | Power | Typical source / context |
|---|---|---|
| +50 | 100 W | High-power amateur radio transmitter |
| +43 | 20 W | Typical VHF/UHF mobile radio |
| +37 | 5 W | Handheld radio (HT) max power |
| +30 | 1 W | Typical smartphone cellular Tx |
| +27 | 500 mW | Bluetooth Class 1 (long range) |
| +20 | 100 mW | Wi-Fi access point (typical) |
| +10 | 10 mW | Bluetooth Class 2 |
| 0 | 1 mW | Reference level; low-power IoT Tx |
| −10 | 100 µW | Strong received signal (cable) |
| −40 | 100 nW | Moderate received Wi-Fi signal |
| −70 | 100 pW | Typical received Wi-Fi at range |
| −100 | 100 fW | Minimum usable signal (weak DX) |
| −130 | 1 aW | Near thermal noise floor (kTB) |
SPL Calculator & Reference
Reference: 0 dB SPL = 20 μPa (threshold of human hearing). SPL uses a pressure ratio, so: dB SPL = 20 × log₁₀(p / 20μPa).
SNR, Noise Figure & Friis Formula
Friis formula: noise performance of a cascade is dominated by the first stage. A high-gain, low-noise first stage is critical.