Is Roll a Snowman free?

Yes. It runs in your browser on phones, tablets and computers, with no download and no account.

How heavy is a real snowman?

A typical three-ball snowman about 1.5 m tall weighs roughly 100 to 250 kg, most of it in the bottom ball. Packed snow is around 400 to 500 kg per cubic metre.

Why does a snowball get bigger as you roll it?

Each turn presses a layer of fresh snow onto the ball. The volume added per metre is roughly the circumference times the layer thickness, so the radius grows with the square root of the distance rolled.

What is the best snow for building a snowman?

Wet, sticky snow at around 0 °C. Its grains bond quickly by sintering and a little liquid water glues them together. Cold, dry powder will not pack.

What are good snowman proportions?

Each ball about 70% of the width of the one below works well, for example 90, 64 and 46 cm across. The game shows the ideal sizes as dashed circles.

Roll a Snowman

Roll it, stack it, dress it. Then watch it wave. Back to the game

How to play

Push the little snowball around the field by dragging toward where you want it to go, or with the arrow keys or WASD. A child in a bobble hat does the pushing. Wherever the ball rolls over fresh snow it picks up a layer and grows, leaving a green track of bare grass behind it. When a ball is the size you want, press Keep this ball (or Enter) and a new one appears. Roll three: a bottom, a middle and a head. The dashed circles in the corner show good proportions for this field, and the solid circles show what you have so far.

Then stack them. Tap the screen, press Heave! or hit Space when the needle on the strength meter swings into the green. Heavier balls need more heaves and give you a smaller green zone. Last, dress your snowman: drag the coal eyes, carrot nose, stick arms, buttons, scarf and hat onto it. Things click into place when they are close to the right spot, but you can put them anywhere on the snow. On a keyboard, N places the next decoration, the arrow keys nudge it and Enter brings the snowman to life. Watch it blink, smile and wave, and see who comes to visit.

Each field has a gentle timer. When the sun comes out, unfinished balls start to melt a few millimetres at a time, so keep rolling. Rocks and fence posts knock chunks off your ball, slush is sticky, and on the hill the ball will roll away downhill if you let go. Your score adds up size, proportions and decorations, out of 300.

Why a snowball grows (and why it slows)

As a ball rolls, it presses a strip of snow onto its belt. If it picks up a layer of thickness t around its circumference, every metre rolled adds a volume of about dV = 2πr · t · ds. Since a sphere’s volume is V = 4/3 πr³, that works out to r² = r₀² + t · s: the radius grows with the square root of the distance. Doubling the size of a ball takes about four times as much rolling, which is exactly how it feels in a real garden.

Its mass grows much faster. Mass is density times volume, m = ρ · 4/3 πr³, so a ball twice as wide is eight times as heavy. Fresh powder is mostly air, around 50 to 200 kg per cubic metre, but rolling and squeezing packs it to about 400 to 500 kg/m³. A bottom ball 90 cm across therefore weighs about 160 kg, and a whole snowman of that size is roughly 250 kg. In the game you push with a steady effort, the snow squashes under the ball (rolling resistance of about a tenth of its weight), and heavy balls take a long time to get moving and to turn.

Why snow packs at all

Snow sticks to itself through sintering: where two ice grains touch, water molecules move to the contact and build a little neck of ice that bonds them. It happens fastest near the melting point, which is why mild days around 0 °C make the best snowmen. Snow that warm also holds a little liquid water, from a trace up to several percent by volume, which acts like glue between grains and refreezes into bonds. Very cold, dry powder has no such glue and falls apart in your mittens, while slush is so wet and heavy that the ball just smears.

Tips

Roll the bottom ball first and biggest. The game sorts the balls by size when you stack them.
Aim for each ball to be about 70% the width of the one beneath it.
Roll in big loops over fresh, white snow. Retracing your green track adds nothing, though falling snow slowly covers it again.
Start heavy balls moving before you steer them, and keep away from rocks.

If you love snow, grow your own crystal in ../grow-a-snowflake/ or take a sledge down a hill you draw in ../draw-a-sled-track/.

Questions people ask

Is Roll a Snowman free?: Yes. It runs in your browser on phones, tablets and computers, with no download and no account.
How heavy is a real snowman?: A typical three-ball snowman about 1.5 m tall weighs roughly 100 to 250 kg, most of it in the bottom ball. Packed snow is around 400 to 500 kg per cubic metre.
Why does a snowball get bigger as you roll it?: Each turn presses a layer of fresh snow onto the ball. The volume added per metre is roughly the circumference times the layer thickness, so the radius grows with the square root of the distance rolled.
What is the best snow for building a snowman?: Wet, sticky snow at around 0 °C. Its grains bond quickly by sintering and a little liquid water glues them together. Cold, dry powder will not pack.
What are good snowman proportions?: Each ball about 70% of the width of the one below works well, for example 90, 64 and 46 cm across. The game shows the ideal sizes as dashed circles.