Hamilton Digital MediaLimited

Tools & calculators

Useful tools for everyday questions.

Practical calculators for hobbies, home projects, and everyday planning. Built by Brian Hamilton and published by Hamilton Digital Media Limited, alongside our puzzle games, apps, and books.

The Toolbox collection

Find your Toolbox.

Explore our 8 calculator websites. Each Toolbox brings together practical tools for its own activity and audience.

8 m4 m1.5 m8 × 4 × 1.5 = 48 m³— L48,000 L
Pool
volume
  • Measure
  • Fill
  • Result
Calculate

pooltoolbox.com

PoolToolbox

Pool and spa calculators for water chemistry, dosing, equipment sizing, and running costs.

BREWGRAVITYSTART · OG—1.050FINISH · FG—1.010(1.050 − 1.010) × 131.25ESTIMATED ABV— %5.25%
Gravity
& ABV
  • Start
  • Finish
  • ABV
Calculate

brewtoolbox.com

BrewToolbox

Brewing calculators for gravity, alcohol content, mash water, hops, fermentation, and packaging.

TANK WATER—100 LACTUAL FLOW—400 L/h400 L/h ÷ 100 LTURNOVER EXAMPLE— / hour4× / hour
Filter
flow
  • Tank
  • Flow
  • Turnover
Calculate

aquariumtoolbox.com

AquariumToolbox

Freshwater, planted, and reef aquarium tools for tank volume, water changes, dosing, and equipment sizing.

10 m5 m10 m × 5 m— m²50 m²
Lawn
area
  • Length
  • Width
  • Area
Calculate

lawntoolbox.com

LawnToolbox

Lawn and garden calculators for seed, fertiliser, soil, mulch, irrigation, and seasonal planning.

FRONT— teeth48 teethREAR— teeth16 teethREAR TURNS1231 crank turn48 ÷ 16— : —3:1
Gear
ratio
  • Front
  • Rear
  • Ratio
Calculate

pedaltoolbox.com

PedalToolbox

Practical cycling calculators and tools for riders.

3-DEVICE EXAMPLERVLEDs10 W × 4 hFan20 W × 3 h12 V TV40 W × 2 hDAILY USEWh / day040100180
Daily
use
  • Lights
  • Fan
  • TV
Calculate

rvingtoolbox.com

RVingToolbox

Practical calculators and planning tools for RV owners and travellers.

LOAF LENGTH— cm20 cmBAR THICKNESS— cm2.5 cm1234567820 cm ÷ 2.5 cm— bars8 bars
Soap
bars
  • Loaf
  • Cut
  • Bars
Calculate

soapmakingtoolbox.com

SoapmakingToolbox

Soapmaking calculators for lye, recipe building, batch sizes, mould volume, and cost per bar.

FRACTIONALDECIMAL—5/2—3.505 ÷ 2 + 1—%28.6%1 ÷ 3.50IMPLIEDPROBABILITY
Odds
maths
  • Odds
  • Decimal
  • Implied
Calculate

bettoolbox.co.uk

BetToolbox

Sports betting calculators for understanding odds and probability.

Behind the tools

From puzzle systems to practical calculators.

Building puzzle websites also means building the solvers, generators, and helpers that make them useful. Brian's interest in turning rules and calculations into approachable software extends to the everyday questions these Toolbox sites help answer.

Brian has an internet engineering degree and 30 years of development experience. His earlier quantitative software work included building mathematical models for sports prediction companies. That background informs his approach to implementing formulas, checking calculations, and explaining results.

The subject knowledge behind a calculator matters too. Our approach is to make the sources, assumptions, and limits clear, so people can understand how a result applies to their own situation.

Meet Brian HamiltonOur publishing standards

Puzzles & games

Explore our puzzle work.

Puzzles remain at the heart of Hamilton Digital Media: browser games, Android apps, and printed books built around logic, strategy, and the pleasure of working something out.

Explore puzzles & games

Questions & corrections

Help us improve a tool.

Tell us about a calculation that needs a closer look, an explanation that could be clearer, or a tool you would find useful. For a calculation issue, include the page, input values, units, and result so we can follow your example.

Get help with a tool