What gives a lawn bowl its curve?
Officials' detail · The green, the equipment and sets play · 2 of 2A bowl's curve, its bias, comes from its shape, not a weight inside. Each player uses a set of four matching bowls, 112 to 131 mm across for composition bowls and no heavier than 1.59 kg, carrying a World Bowls stamp that shows the bias meets the minimum. The jack is a white or yellow ball about 63 mm across.
How it works
- Bias: the curved path; the more rounded side, marked with small rings, is the bias side.
- A set: four bowls of the same make, model, size, weight, colour, bias and serial number.
- Size and weight: composition bowls 112 to 131 mm across, wooden 112 to 134 mm; at most 1.59 kg.
- Minimum bias: at least that of the Working Reference Bowl.
- Stamp: the World Bowls Stamp on the bias side, showing the year it expires; re-test at least every 10 years.
- No tampering: altering a stamped bowl's bias means suspension.
- Markings: stick-on markings may help tell sets apart; same design for a whole team.
- The jack: white or yellow; 63 to 64 mm and 225 to 285 g on grass, 63 to 67 mm and 382 to 453 g on synthetic or indoor greens.
- Challenges: not during a game; lodged within 10 minutes after the final end, with a deposit; bowls that fail mean the game is forfeited.
The glossary has the bias, the bowl, the jack, the World Bowls Stamp, the Working Reference Bowl and the challenge to bowls.
Tricky cases
Is there a weight inside a bowl that makes it curve?
No. The laws define the bias as coming from the bowl's shape.
Can a player use three bowls from one set and one from another?
Not in the game. A player must use bowls from the same set. In trial ends, any mix is allowed.
A player suspects the opponent's bowls are illegal. Can they challenge mid-game?
No. A player who challenges during the game is disqualified. A challenge is lodged afterwards, within 10 minutes.
Can a bowler colour in the rings on a bowl?
Yes. Colouring the grooves or dimples for decoration is allowed.
Why the rule exists
A minimum bias keeps every bowl curving enough that line matters.
Where it differs
| Where | What changes | Source |
|---|---|---|
| Bowls | Size, weight, bias, stamp | WB Laws 52, 53 |
| Jack | Sizes by surface | WB Law 51 |
| Mat | 600 by 360 mm | WB Law 50 |
From the rule book
World Bowls, Laws of the Sport of Bowls, Crystal Mark Fourth Edition (August 2022), Definitions D.1 to D.4 and Laws 2.4 and 50 to 53. Checked 14 October 2026. Official document: the World Bowls Laws of the Sport of Bowls.