dB Calculator – Decibel to Ratio Converter for Audio and RF

Convert between decibels and linear ratios for power, voltage, and amplitude. Our dB calculator is essential for audio engineering, RF systems, and signal processing.

Decibels (dB)

How to Use This dB Calculator

Select your conversion type

Choose between dB to Ratio, Ratio to dB, or dBm calculations using the tabs at the top.

Enter your value

Input the decibel value, ratio, or power in milliwatts depending on your selected conversion type.

Click the appropriate calculate button

Select Power Ratio or Voltage Ratio for dB conversions. The result appears instantly below.

Common dB Values Reference

dB	Power Ratio	Voltage Ratio	Application
-3 dB	0.5	0.707	Half power point (cutoff)
0 dB	1	1	Reference level (no change)
3 dB	2	1.414	Double power
6 dB	4	2	Double voltage
10 dB	10	3.162	10x power
20 dB	100	10	10x voltage
30 dB	1,000	31.62	1000x power

Power uses 10^(dB/10). Voltage uses 10^(dB/20) because power is proportional to voltage squared.

Understanding Decibels

What Is a Decibel?

A decibel (dB) is a logarithmic unit expressing the ratio between two values. It's not an absolute measurement like volts or watts — it's a comparison. 0 dB means no change. Positive dB means gain. Negative dB means loss.

Power vs Voltage Decibels

Power ratios use 10 × log10(ratio). Voltage ratios use 20 × log10(ratio) because power equals voltage squared divided by resistance. Doubling voltage quadruples power, hence the factor of 20 instead of 10.

What Is dBm?

dBm is decibels relative to 1 milliwatt. It's an absolute power level, not a ratio. 0 dBm = 1 mW. 10 dBm = 10 mW. 30 dBm = 1 watt. RF engineers use dBm to specify signal levels and transmitter power.

Why Use Logarithms?

Audio and RF signals span enormous ranges — from microwatts to kilowatts. Logarithms compress this range into manageable numbers. Adding dB values is easier than multiplying ratios. A 10 dB amp followed by a 3 dB loss equals 7 dB total gain.

Tips for Working with Decibels

Memorize Key Values

3 dB = 2x power. 10 dB = 10x power. 20 dB = 100x power. These benchmarks let you estimate quickly without a calculator.

Add dB, Multiply Ratios

When cascading stages, add dB values: 20 dB amp + (-3 dB cable loss) = 17 dB total. To find the combined ratio, convert back from dB.

Watch Your Reference

dBV uses 1 volt reference. dBu uses 0.775 volts. dBm uses 1 milliwatt. dB SPL uses 20 micropascals. Always check which reference applies to your calculation.

Negative dB Means Loss

-10 dB isn't an error — it means the output is 10 times smaller than the input. Attenuators, cable losses, and filter rejection are all expressed as negative dB.

Frequently Asked Questions

Why is there a difference between power and voltage dB?

Power is proportional to voltage squared (P = V²/R). When you double voltage, power quadruples. So 6 dB represents 2x voltage but 4x power. The formulas account for this: 10×log for power, 20×log for voltage.

What does 0 dB mean?

0 dB means the ratio equals 1 — no change. Output equals input. It doesn't mean "no signal" — it means the signal level is unchanged from the reference point.

How do I convert dBm to watts?

Watts = 10^((dBm - 30) / 10). Or remember: 30 dBm = 1 W, 0 dBm = 1 mW, -30 dBm = 1 μW. Each 10 dB change multiplies power by 10.

Can decibels be negative?

Yes. Negative dB indicates a ratio less than 1 — attenuation or loss. -3 dB means half the power. -20 dB means 1/100th the power. Negative values are common for losses and filter rejection.

What's the difference between dB and dBA?

dB is a raw ratio. dBA applies a frequency weighting that mimics human hearing sensitivity. dBA is used for noise measurements. A-weighting reduces low and very high frequencies where human ears are less sensitive.

Other Free Tools

Search tools