Calculators and timers for lifting and running. Work backwards from a goal race time, or turn a one-rep max into a full set-by-set weight table.
«Go heavy today» and «run hard» mean a different intensity every time you execute them. For a plan to be repeatable the intensity has to be a number, and producing that number is what these calculators do: set weights from a one-rep max, training paces from a goal time, work and rest blocks from an interval spec.
The point is the ratio, not the absolute. Whether your one-rep max is exactly right matters less than whether today's set landed at 70% of it.
Actually measuring a one-rep max means attempting a true maximum, which carries injury risk and costs days of recovery. So it is normally derived backwards from «how many reps at this weight», using formulas such as Epley, Brzycki or Lombardi.
These formulas are accurate when the rep count is low. Between three and six reps they agree closely; past twelve they diverge from each other and from reality. Enter a set performed at five reps or fewer whenever you can.
It also depends on the lift. Compound movements like the squat and deadlift hold up reasonably at higher reps, while the bench press and single-joint work fatigue faster and tend to be overestimated.
Know two and the third follows. In practice the useful direction is «goal finish time → required pace per kilometre»: a 1:50 half marathon needs roughly 5:12 per kilometre.
The common mistake here is using the average pace as the opening pace. Most runners slow in the second half, so if the target average is 5:12 you have to start slightly slower than that for the average to come out right.
Training paces are a separate layer. A recent race result sets your current fitness, and easy, tempo and interval zones are derived from it — mixing those zones produces more adaptation than running every session at one speed.
Interval training is the general name for alternating defined work and rest blocks. Eight 400s with 90 seconds recovery, three minutes running and one walking — all intervals. Block length and work-to-rest ratio change with the goal.
Tabata is one very narrow case of it: 20 seconds all-out, 10 seconds rest, eight rounds, four minutes total, and the original study assumed an intensity around 170% of VO₂max. A comfortable session that borrows the name is a different workout from the protocol.
That is why the timer here lets you set work, rest and rounds yourself. Matching the blocks to your own capacity matters more than matching a famous specification.
Exercise energy estimates multiply body mass, duration and an intensity value (MET) taken from a standard table. Those MET values describe an average person performing a standard movement. Real expenditure shifts with body size, efficiency, terrain and temperature.
Practically, it is better not to eat back a calculated burn — the estimation error easily exceeds a meal. Use the figure as a relative measure for comparing sessions instead.
They do not design a training programme and do not assess injury or pain. They cannot see recovery status, sleep, nutrition or injury history — all of which decide what today's intensity should actually be.
In particular, do not walk up to a bar and attempt an estimated one-rep max. An estimate is a planning baseline, not a guarantee of what you can lift today. If something hurts or you are rehabilitating, a professional's prescription comes first.
Body weight, race times and training loads are never transmitted. Both the timers and the calculators run inside the browser and work without an account. Some tools also offer a screen-wake option for sessions where the timer has to keep running untouched.