Free Space Path Loss Calculator – Path Loss in dB from Distance and Frequency

Use the free tool above, then read on for how it works, a worked example, and practical tips.

What this tool does

Even with a perfect clear path, a radio signal weakens as it spreads out, and free space path loss puts a number on that spreading. This calculator turns distance and frequency into path loss in decibels and an expected received power, giving you the baseline every link budget starts from.

How it works

The tool uses the standard free space formula with distance in kilometres and frequency in megahertz: loss in dB equals 20 times log10 of distance plus 20 times log10 of frequency plus 32.44. Doubling the distance adds about 6 dB of loss, and doubling the frequency adds about 6 dB too, which is why higher bands need more gain for the same range.

How to use it

Enter your values in the boxes above.
Press the calculate or play button.
Read the result shown below the tool.
Try a second set of values to compare options.

Worked example

At 10 kilometres and 145 MHz the free space loss is about 95.7 dB, so a 30 dBm transmitter, about one watt, arrives near minus 65.7 dBm before any antenna gain. Stretch the same link to 100 kilometres and the loss rises by 20 dB, which shows why distance dominates link budgets so quickly.

Practical tips

Start every link budget from this free space figure, then add antenna gains and subtract extra losses for cables, buildings, and trees to reach a realistic received level. If the result sits close to your receiver’s sensitivity, add margin for fading rather than trusting the free space number alone.

Common mistakes

A common mistake is mixing units, such as entering miles into the kilometre formula or gigahertz into the megahertz formula, which shifts the answer by tens of decibels. Another is treating free space loss as the whole story, when real paths always add extra loss from ground, foliage, and obstacles.

Questions and answers

Is this tool free? Yes. It runs in your browser, needs no account, and gives instant results.

Do I need to install anything? No. The tool works on any modern phone or computer browser.

How accurate are the results? The maths follows the standard formulas shown above. Real-world results vary with terrain, equipment, and conditions, so use the figures for planning.

Can I use it on my phone? Yes. The tool is designed to work on a phone screen, so you can use it at the operating desk, in the field, or at a club station without a computer.

Who uses this tool

Radio amateurs, students, and club members all use tools like this one, because they turn a formula from a book into an answer for your own station in seconds. Beginners use it to check homework and first setups, while experienced operators use it to sanity-check a plan before spending money on cable, masts, or antennas. Even a quick check can prevent a costly mistake, such as ordering the wrong cable length or aiming a beam in the wrong direction.

What to try next

Run the tool with your real station values, not just the default numbers, so the answer means something for your setup.
Change one input at a time and watch how the result moves, because that shows you which input matters most.
Write the result in your station notebook next to the date, so you can compare later changes against a known baseline.

Safety note: this is an educational estimator only. Real transmissions need an amateur licence and must follow your local regulations, band plans, and power limits. Never transmit without the proper licence, and treat every result here as a planning guide, not professional or legal advice.

Versión en español: Calculadora de Pérdida en el Espacio Libre – Pérdida de Trayectoria en dB según Distancia y Frecuencia