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Circuit Lab

A free circuit builder for grades 3–12. Students drag real parts between the dots on a board, and Circuit Lab works out what the electricity does: bulbs light, motors spin, and moving dots show the current.

  • Free
  • Grades 3–12
  • 19 parts
  • Series and parallel
  • No sign-up
Circuit Lab with a 1.5 V battery and two bulbs side by side in parallel on the dot board. Both bulbs glow and read Bright, yellow dots run along the wires, and the bar above the board says It works! The loop is closed, so electricity flows from + all the way around to −. The Parts tray on the left lists Wire, Battery, Bulb, Switch, Button, Motor, Buzzer, Material, Magnet, Resistor, LED, Dimmer, Fuse, Solar cell, Ammeter and Voltmeter.

Build a circuit and see whether it works

A teacher on TikTok asked for an app where students build series and parallel circuits with bulbs, batteries and switches, and practice predicting whether a circuit will work. In Circuit Lab, every part snaps between two dots, so circuits stay tidy on a projector. Circuit Lab solves the whole circuit after every change, so the answer to "will it work?" is always the true one. Pick grades 3–5, 6–8 or 9–12, and the parts, numbers and words change to fit your class.

Launch Circuit LabSee how it works ↓

From an empty board to a working circuit

  1. Circuit Lab set to grades 3–5 with the Start from menu open. Under Starter circuits for grades 3–5 are Simple loop, Series (ticked), Parallel, Motor + buzzer, Electromagnet and Test materials, then Clear the board. The Parts tray shows nine parts: Wire, Battery, Bulb, Switch, Button, Motor, Buzzer, Material and Magnet.

    Pick a grade and a starter circuit

    Choose 3–5, 6–8 or 9–12 at the top. Start from an empty board, or open Start from for a ready-made circuit for that grade, such as Series, Parallel, Electromagnet or Test materials for grades 3–5.

  2. A battery, an open switch and a bulb in one loop. The bulb reads Off, the wires have no moving dots, and the bar above the board says Nothing working yet. There is a gap somewhere. Electricity needs a full loop from + back to −. The panel on the right shows the switch with 0.0 mA through it, State Open, and a Close it button.

    Drag parts onto the board

    Drag a part from the tray and drop it between two dots, or drag from dot to dot to draw a wire. Drag a part off the board to remove it. The bar above the board says what's happening, like "Nothing working yet" when there's a gap in the loop.

  3. Two bulbs in series, both reading Dim, with the first bulb selected. The panel on the right reads Bulb: current through it 0.25 A, 0.74 V push used up here, 0.18 W power to light, Brightness Dim, Electricity going through Some, and the note More current through a bulb makes it brighter.

    Tap a part to see inside it

    Tap any part to see the push it uses, the current through it and, in grades 9–12, its power. The panel also has the part's settings, like a battery's volts or a resistor's value, and a short note on what's going on.

  4. The Follow the charge tab: one large charge travels along the wire toward a bright bulb. The bar above says Cruising along. The wire barely uses any energy, so the charge keeps what it has. On the right, Close-up: the wire shows the charge gliding between metal atoms, and The charge's energy reads 1.45 V, with Bulb (light) −1.45 V and Battery (push) +1.45 V.

    Follow one charge around the loop

    Open Follow the charge to slow the circuit down and watch one charge go around. A close-up shows what each part is like inside, and an energy bar shows the charge losing push in the bulb and getting it back from the battery. Press Pause or Slow to take your time.

What's in Circuit Lab

Series and parallel you can see

Two bulbs in series share the battery's push, so each one is Dim. Put the same two bulbs in parallel and each gets the full push, so both read Bright. Faster dots on the wires mean more current, so students can compare circuits before they see any numbers.

A 1.5 V battery and two bulbs in a single loop. Both bulbs read Dim and glow faintly, and yellow dots run along the wires.

Everyday parts for grades 3–5

Grades 3–5 get nine parts, including a motor, a buzzer, a push button, an electromagnet that picks up paper clips, and a material tester. Put a paper clip, coin, foil, pencil lead, salt water, eraser, wood, plastic or rubber band in the tester to find out which ones let electricity through. Labels use words like Bright and Picks up 7 clips instead of numbers.

The Test materials starter for grades 3–5: a battery, a bulb and a material tester holding a coin in one loop. The coin reads Coin · yes, the bulb reads Bright, and the bar above the board says It works!
The Electromagnet starter for grades 3–5: a battery, a pressed push button and an electromagnet coil in one loop. Paper clips hang from the coil, which reads Picks up 7 clips, and the button reads Pressed.

Voltage, symbols and more parts for older grades

Grades 6–8 add resistors, LEDs, a dimmer, a fuse, a solar cell, an ammeter and a voltmeter. Grades 9–12 add a capacitor, a transistor and a light sensor. Switch to Voltage to color every wire from 0 V to the battery's full push, and to Symbols to draw parts as circuit diagram symbols. A Light in the room slider sets the light for every solar cell and light sensor on the board.

The Nightlight starter for grades 9–12 in Voltage and Symbols view. A 3 V battery, resistors, a light sensor, a transistor marked B, C and E, and an LED are drawn as circuit symbols, with wires colored from blue at 0 V to orange at 3 V and voltages beside each part. Light in the room is set to 0%, the LED glows red and the transistor reads Fully on.

Built for the classroom

  • Share link copies a link that opens your circuit, ready to post in Google Classroom.
  • Undo and Redo take back any change to the board.
  • Save file keeps a copy of a circuit, and Open file brings it back.
  • The board saves itself in your browser and comes back after a refresh.
  • Each grade has its own starter circuits, from Simple loop to Nightlight.
  • No points, scores or badges: students build and see what happens.

No accounts, and circuits stay on your device

Nobody signs in to Circuit Lab. The board saves only in your browser. A share link holds the circuit itself, so opening one doesn't need an account, and anyone with the link can open that circuit.

Circuit Lab questions

What is Circuit Lab?

A free online circuit builder from Flint for grades 3–12. Students drag batteries, bulbs, switches and other parts onto a board, and Circuit Lab shows what the electricity does.

Is Circuit Lab free?

Yes. Circuit Lab is free, with no sign-up.

Which grades is it for?

Grades 3–12. The grade setting at the top changes the parts in the tray, the starter circuits and how much the labels say. Grades 3–5 mostly see words like Bright and Spinning fast, and from grade 6 the labels add volts, amps and ohms.

Can students build series and parallel circuits?

Yes. Both are starter circuits in every grade. Bulbs in series are dim, and bulbs in parallel stay bright.

What parts are there?

19 in all: wire, battery, bulb, switch, push button, motor, buzzer, material tester, electromagnet, resistor, LED, dimmer, fuse, solar cell, ammeter, voltmeter, capacitor, transistor and light sensor. Grades 3–5 see the first nine, grades 6–8 see 16, and grades 9–12 see all 19.

How do I give students a circuit to work on?

Build or open the circuit, press Share link, and paste the link into Google Classroom or anywhere else you post work. Students open the link and get the same circuit.

Do students need accounts?

No. Students open Circuit Lab in the browser and start building, and their board stays saved in that browser.

Tell us what your class builds

Send an idea, a bug or a part you wish Circuit Lab had. Every message goes to the Flint team that built Circuit Lab.

Sparky in a white lab coat with safety goggles on its head, holding a flask of green liquid.

Ready to build a circuit?

Launch Circuit Lab

Made by Flint